Privacy Policy

Last updated: October 7, 2026

This Privacy Policy explains how DuoFit, the iPhone and Android app that helps two people lose weight together (the "app" or "DuoFit"), handles your personal information: what we collect, why we collect it, who we share it with, how long we keep it, and the choices and rights you have.

Who is responsible. DuoFit is provided by Dzianis Maliush, an individual developer ("we", "us", "our"), who is the controller of the personal information described in this policy. You can reach us at support@duofit.site.

This English version is the official version of this policy. If we provide a translation and it differs from this text, the English version prevails, unless mandatory law where you live requires otherwise.

1. Scope

This policy covers the DuoFit app and our website, including the invite page that opens when someone shares an invite link, and this page. It does not cover services run by other companies that you use together with DuoFit, such as the Apple App Store, Google Play, Sign in with Apple, Google Sign-In, Apple Health or Health Connect. Their own privacy policies apply to them.

2. Information we collect

2.1 Account and sign-in

You sign in with Apple, with Google, or with a sign-in link sent to your email address. Sign-in is handled by Firebase Authentication, a Google service. We receive and store:

• your email address. If you use Sign in with Apple and choose to hide your email, we receive Apple's private relay address instead;
• your Firebase user ID and the DuoFit user ID that our server assigns to you;
• the identifier of the Apple or Google account you signed in with, as part of your sign-in record;
• session tokens that keep you signed in.

Apple or Google may also share the name on your account. The name used in DuoFit is the one you type yourself. Firebase Authentication keeps its own sign-in record for your account, which may include basic profile information that Google shares when you use Google Sign-In, such as your name and a link to your profile photo.

2.2 Profile and daily check-ins

To track your progress, you give us:

• Profile: your first name, height, starting weight, target weight and preferred units (kilograms or pounds, centimeters or feet and inches);
• Daily check-ins: your weight, how many glasses of water you drank, how your food went ("on track", "so-so" or "off track"), whether you worked out, and your step count, together with the date of each check-in;
• Settings: your notification choices and reminder time.

The app also sends your device's time zone and language with each request, and we store them so that "today", reminders and your streak follow your local day.

Your weight, height and check-ins are information about your health. Section 5 explains how we treat it.

2.3 Steps from Apple Health or Health Connect

If you allow it, DuoFit reads today's step count from Apple Health on iPhone, or from Health Connect on Android, and saves it with today's check-in. We read no other type of health data and no step history, and DuoFit never writes anything to Apple Health or Health Connect. You can always type your steps in yourself instead. You can turn access off at any time in the Health app (Sharing → Apps → DuoFit) or in Health Connect settings.

Data from Apple Health (HealthKit) and Health Connect:

• is used only to show your steps in DuoFit, to you and to your partner;
• is never used for advertising or marketing, and is never sold;
• is never shared with third parties, except your partner (because showing your steps to your partner is what you ask DuoFit to do) and the service providers that help us run DuoFit (Section 6), and then only as needed to provide the service;
• is not stored in iCloud.

DuoFit's use of information received from Health Connect complies with the Health Connect Permissions policy, including its Limited Use requirements.

2.4 Couple, shared goal and stakes

• Pairing: when you create a couple, we generate a 6-character invite code and a link you can share. We store which two accounts are paired, when the couple started and, if it ends, when it ended.
• Shared goal: how much you plan to lose together, by what date, and each partner's starting point for the goal.
• Streak: your shared streak is calculated from both partners' check-ins.
• Stakes: the favors you and your partner propose to each other, either one of our ready-made options (such as "Cook dinner") or your own text of up to 40 characters; their status (proposed, agreed, declined or ended); and the days on which a favor became owed and whether it was done or let go.

Your own stake text is checked automatically before it is saved. Links, email addresses, phone numbers, money amounts, currency symbols and words from a list of offensive words are not accepted.

2.5 Subscriptions and purchases

You buy subscriptions through the Apple App Store or Google Play. We never see or store your card or other payment details. We use Adapty to manage subscriptions. Adapty receives your DuoFit user ID, your purchase and subscription history from the store, and technical information about your device, such as the device model, operating system, app version and IP address.

Our server stores the date your free week ends and keeps a copy of your subscription status (for example, the product, start and expiry dates, the store and the store's transaction ID), so that it can decide whether your couple has access.

2.6 Push notifications

If you allow notifications, we store your device's push token and whether it is an iPhone or an Android device. Notifications are sent through Firebase Cloud Messaging, a Google service, and on iPhone through the Apple Push Notification service. A notification can include your partner's name, your streak and the name of a ready-made stake. It never includes weight, step counts or stake text that someone wrote themselves. Notifications can appear on your lock screen, where people near you may see them. So that each notification is sent only once, we keep a short record of the notifications we've sent (their type and date) for 14 days.

2.7 Analytics and crash reports

• Firebase Analytics (Google) helps us understand how DuoFit is used so we can improve it. It receives events about actions in the app, such as signing up, joining a couple, sharing an invite, opening the subscription plans or buying a subscription, together with your DuoFit user ID. It also collects some information automatically, such as an app instance ID, device model, operating system, app version, approximate location (country or region, derived from your IP address) and session information.
• Amplitude receives the same app events with your DuoFit user ID, plus when a session starts and ends and when the app is installed, opened or updated, and the device model, operating system, app version, language and country. We configure Amplitude not to collect your IP address, city, mobile carrier or any advertising identifier.
• Sentry receives crash and error reports from the app and from our server: what went wrong and where, the device model, operating system, app version and your DuoFit user ID. We configure Sentry not to collect IP addresses or other personal information by default.

We never send your weight, height, steps, other check-in values or the text of your stakes to analytics or crash reporting.

2.8 Technical data and server logs

When the app connects to our server, the server receives technical information such as your IP address, the date and time, the request made, the app version and the platform. Our web server logs IP addresses. Our application logs record each request, its result and your DuoFit user ID, but never the content of your check-ins. We use logs to run DuoFit, fix problems and keep it secure. Our server also uses IP addresses briefly, in memory, to limit repeated requests.

2.9 Messages to support and reports

If you email us, for example to ask a question, exercise your privacy rights or report a stake, we receive your email address and whatever you write. When you tap "Report this stake", DuoFit opens a pre-filled email in your mail app with the stake's ID and text. Nothing is sent until you send that email.

2.10 Information stored on your device

The app keeps your sign-in tokens in your device's secure storage (the Keychain on iPhone, Keystore-protected storage on Android) and a few small settings in regular app storage: for example, which introduction screens you've seen, an invite code you opened before signing in (kept for up to 24 hours), and your email address while an email sign-in link is pending. Your check-ins are not stored on the device; the app loads them from our server.

2.11 Our website

Our website, including this page and the invite page, does not use cookies, analytics or advertising. Like any website, the server that delivers the pages receives your IP address and browser information, which may be kept in its logs for security. The pages load a font from Google Fonts, so Google receives your IP address when a page loads. The invite page shows the invite code from the link and collects nothing else.

3. What your partner can see

DuoFit exists so that two people can follow each other's progress. When you pair with someone, they can see:

• your first name;
• your starting, current and target weight, and your progress toward your target;
• your check-ins (weight, water, food, workout and steps), including whether you've checked in today;
• your weight chart and statistics for the last 7 or 30 days, such as weight change, number of check-in days, average water and steps, and workouts. This includes days before you paired that fall within that period;
• your shared streak, your shared goal and your combined progress;
• the stakes you propose or agree to, and any favor that is owed;
• whether your subscription covers the couple;
• notifications about your activity, for example when you check in, join or leave the couple, or respond to a stake.

Your partner does not see your email address, your height, how you sign in or your payment details.

Before someone joins your couple, the app shows them your first name, so share your invite link or code only with the person you want to pair with. You can be in only one couple at a time, and a couple has two people.

When the couple ends, because either of you leaves or deletes their account, your former partner can no longer see any of your information in the app. Notifications that were already delivered stay on their device.

4. How we use your information and our legal bases

We use your information only for the purposes below. Where the EU or UK General Data Protection Regulation (GDPR) applies, each purpose relies on the legal basis shown:

• To provide DuoFit: your account, profile, check-ins, couple, streak, shared goal, progress, stakes, reminders and partner notifications. Legal basis: performance of our contract with you (the Terms of Use).
• To process your health data (weight, height, check-ins and steps), including showing it to your partner. Legal basis: your explicit consent (Section 5).
• To read steps from Apple Health or Health Connect. Legal basis: your explicit consent, given through the system permission.
• To provide the free week and subscriptions: checking who has access, restoring purchases and making sure each person gets the free week only once. Legal basis: performance of a contract, and our legitimate interest in preventing misuse of the free week.
• To understand how the app is used, fix crashes and improve DuoFit (analytics and crash reports). Legal basis: our legitimate interest in a reliable and useful app, and your consent where the law requires it.
• To keep DuoFit safe and secure: preventing abuse, fraud and unauthorized access, handling reports about stakes and enforcing our Terms of Use. Legal basis: our legitimate interests.
• To answer your messages and requests. Legal basis: performance of a contract and our legitimate interests, and a legal obligation when you exercise your privacy rights.
• To comply with the law and to establish, exercise or defend legal claims. Legal basis: legal obligation and our legitimate interests.

We don't use your information for advertising. We don't make decisions about you based solely on automated processing that have legal or similarly significant effects on you. Where we rely on legitimate interests, you can object (Section 11).

5. Health data

Your weight, height, check-ins and steps are health data, which many laws treat as sensitive. We use them only to provide DuoFit to you and your partner: to show your progress, calculate your streak and shared goal, and check that your target weight stays within the limits described in the Terms of Use. We never use health data for advertising, never sell it, and never send it to analytics or crash reporting.

Where the GDPR applies, we process health data on the basis of your explicit consent. You give it when you enter the data in the app, and when you pair with a partner after the app has told you what your partner will see. You can withdraw your consent at any time: leave the couple (your former partner then no longer sees your data), turn off Health access, or delete your account. Withdrawing consent does not affect processing that happened before. DuoFit cannot work without health data, so to stop all processing, delete your account.

6. Who we share information with

6.1 Your partner

Your partner sees the information listed in Section 3. That is the purpose of DuoFit, and it happens only after you pair.

6.2 Service providers

We use the following providers to run DuoFit. They process information on our behalf and under our instructions, except Apple and Google as app stores and platform providers, which act under their own terms and privacy policies:

• Google (Firebase): sign-in (Firebase Authentication, including sending email sign-in links), push notifications (Firebase Cloud Messaging), app analytics (Firebase Analytics), and the page that completes email sign-in links (Firebase Hosting); and Google Fonts on our website.
• Adapty: subscription management, including checking purchases, keeping subscription status and showing the subscription plans.
• Sentry: crash and error reports.
• Amplitude: app analytics.
• Apple and Google: app distribution, in-app purchases, Sign in with Apple, Google Sign-In, delivery of push notifications, and Apple Health or Health Connect on your device.
• Our hosting provider: runs our server, which serves our website, and our database, and stores backups.
• Our email provider: handles messages sent to our support address.

6.3 Legal reasons and transfers of DuoFit

We may disclose information if the law requires it, to respond to valid legal requests, or to protect the rights, safety and property of our users, other people or DuoFit. If DuoFit is transferred to a new owner, for example as part of a sale, your information may be transferred to that owner, who must protect it as described in this policy.

6.4 No advertising, no tracking, no sale

DuoFit has no ads and no advertising or attribution tools. We don't track you across apps and websites owned by other companies, we don't ask for permission to track you, and we don't access your device's advertising identifier (the IDFA on iPhone or the Advertising ID on Android). We don't sell your personal information, and we don't share it for targeted (cross-context behavioral) advertising.

7. International transfers

We, our service providers and your partner may be in different countries. Your information may be processed in the United States, the European Economic Area and other countries whose data protection laws may differ from those where you live. When we transfer personal data from the EEA, the UK or Switzerland, we rely on an adequacy decision (such as the EU–U.S. Data Privacy Framework, where the recipient is certified under it) or on the Standard Contractual Clauses approved by the European Commission and their UK equivalent. You can ask us for more information about these safeguards.

8. How long we keep information

We keep personal information only as long as we need it:

• Account, profile, check-ins, stakes and subscription status: as long as your account exists. They are deleted when you delete your account (Section 9).
• Ended couples: when a couple ends, its shared streak, goal and stakes stop and disappear from the app. The record of the ended couple stays linked to your account, where nobody can see it, and is deleted when you delete your account.
• Session tokens: each expires within 90 days; expired tokens are removed every day.
• Push tokens: until you sign out, the token stops working, or you delete your account.
• Record of sent notifications: 14 days.
• Analytics data: up to 14 months in Firebase Analytics; in Amplitude, until you delete your account (Section 9).
• Crash reports: up to 90 days (Sentry).
• Server logs: a short period. Logs are rotated and overwritten automatically.
• Backups: our server makes one database backup a day and keeps the 7 most recent, so deleted data disappears from these backups within 7 days.
• Support emails: as long as we need them to handle your request and keep a record of it.
• Free-week record and deletion records after you delete your account: see Section 9.3.

9. Leaving a couple and deleting your account

9.1 Leaving a couple

You can leave your couple at any time in Settings → Leave couple. The couple then ends for both of you: the shared streak, the shared goal and all stakes are cleared, and any favor still owed is cancelled. Each of you keeps your own profile and check-in history. Your partner gets a notification. If your partner's subscription covered you, you lose that access, and the same applies to your partner if yours covered them.

9.2 Deleting your account

You can delete your account in the app at any time in Settings → Delete account. The option is also in the account menu before you pair and on the screen shown when access has ended. If you signed in with Apple, you'll be asked to confirm with Apple, and DuoFit's access to your Apple ID is revoked.

When you delete your account:

• your couple ends and your partner gets a notification;
• your profile, check-ins, stakes, couple memberships, push tokens, sessions and subscription status are deleted from our database immediately;
• we delete your Firebase Authentication account, your Adapty profile and your analytics data in Amplitude. If any of these services is temporarily unavailable, we retry automatically every day. Until all three deletions are confirmed, we keep only the identifiers needed to finish them (your Firebase user ID and your DuoFit user ID).

9.3 What we keep after deletion

• Free-week record. So that each person gets the free week only once, we keep a one-way cryptographic hash (SHA-256) of each identifier you signed in with, meaning your Apple or Google account ID and your email address, together with the date your free week ended and the date of the record. We can't read your email address or account ID from the hash, but if you sign up again with the same identifier, the same hash is produced and we can tell that the free week was already used. We keep this record only if your free week had started, we use it for nothing else, and we keep it for as long as we offer a free week to new users. Legal basis: our legitimate interest in preventing misuse of the free week.
• Backups and logs, until they are overwritten (Section 8).
• Firebase Analytics and crash data linked to your former DuoFit user ID, until they expire (Section 8). They don't contain your name, email address or health data.
• Information we must keep by law, for example a record of a privacy request or information needed for a legal claim.

Deleting your account does not cancel a subscription. Cancel it in your App Store or Google Play account settings, preferably before you delete your account. Apple and Google keep their own records of your purchases under their own privacy policies.

10. Security

We protect your information with measures that suit its sensitivity, including:

• encryption in transit (HTTPS with TLS 1.2 or later) for all traffic between the app and our server;
• short-lived access tokens, and sign-in tokens kept in your device's secure storage;
• a database that cannot be reached from the internet and that only DuoFit's developer can access;
• backup files that only the server's administrator can read.

No system is completely secure. If a security breach affects your personal information, we will notify you and the authorities where the law requires it.

11. Your rights and choices

11.1 Choices in the app

• Change your name, units, height and target weight in Settings → Edit profile.
• Edit today's check-in as often as you like. Past days can't be changed in the app; contact us if something needs correcting.
• Turn notifications on or off in Settings → Notifications or in your device settings.
• Turn Health access on or off in the Health app or in Health Connect.
• Decline or opt out of any stake, and remove your own stakes.
• Leave your couple or delete your account (Section 9).

11.2 Your rights

Depending on where you live, you may have the right to:

• access your personal information and get a copy of it, including in a portable, machine-readable format;
• correct inaccurate information;
• have your information deleted;
• restrict or object to our processing, including processing based on legitimate interests;
• withdraw your consent at any time, without affecting processing that happened before;
• not be treated differently for exercising your rights;
• complain to a data protection authority: in the EEA, the authority in the country where you live or work; in the UK, the Information Commissioner's Office.

11.3 US state privacy laws

California and other states. Depending on your state, you may have the right to know what personal information we collect, use and disclose; to access, correct and delete it; and to opt out of its sale, of its sharing for targeted advertising, and of profiling. We don't sell or share personal information, and we don't use it for targeted advertising or profiling. We use sensitive personal information (health data and account sign-in details) only to provide DuoFit and for other purposes the law allows. The categories of personal information we collect are those in Section 2: identifiers (such as your email address and user IDs), customer records, commercial information (subscription history), internet or other electronic network activity (app usage and logs), and sensitive personal information (health data and sign-in details). We disclose them only to the recipients in Section 6, for the purposes in Section 4.

Consumer health data (for example, Washington and Nevada). Sections 2, 3, 5 and 6 describe the health data we collect, why we collect and use it, and who we share it with: only your partner, at your direction, and the service providers that run DuoFit. You can access or delete your health data and withdraw your consent as described in this section.

11.4 How to make a request

Email support@duofit.site from the address linked to your DuoFit account, or tell us which address that is. We may ask for information to confirm that the request comes from you. We answer within one month, or within the period the law where you live sets (for example, 45 days under US state laws), and may extend that period where the law allows. Where the law allows, you can use an authorized agent; we may ask for proof of their authority. If we decline a request, we'll tell you why and how you can appeal.

12. Children

DuoFit is not directed to children. To use DuoFit you must be at least 16 years old, or older if the law where you live sets a higher age for consenting to the processing of your personal data. We do not knowingly collect personal information from anyone younger. If you believe that a child has given us personal information, contact us and we will delete it.

13. Health disclaimer

DuoFit is a wellness app, not a medical device, and it does not give medical advice, diagnosis or treatment. Talk to your doctor before you start a weight-loss program. See the Terms of Use for details.

14. Changes to this policy

We may update this policy when DuoFit or the law changes. We will change the "Last updated" date at the top. If a change is significant, we will tell you in the app or by email before it takes effect, and where a change requires your consent, we will ask for it.

15. Contact us

Questions about this policy or about your information: support@duofit.site. DuoFit is provided by Dzianis Maliush, individual developer.

See also: Terms of Use