Terms of Service

Effective 25 July 2026 · Version 1.0

These terms govern your use of the Sums mobile application. By installing or using the app you accept them. If you do not accept them, do not use the app.

1. Who provides the service

Sums is provided by Gleb Matsko, an individual developer based in Serbia ("we", "us"). A postal address is available on request. Contact: support@sums.day.

2. Who may use it

You must be at least 16 years old, or the minimum age of digital consent in your country if that is higher. The app is designed for adults and is not directed at children.

3. Your licence

We grant you a personal, non-exclusive, non-transferable, revocable licence to use Sums on devices you own or control, for your own non-commercial use. You may not:

• copy, sell, rent, sublicense or redistribute the app;
• reverse engineer, decompile or attempt to extract the source code, except where that restriction is prohibited by law;
• interfere with the service, submit falsified results, or attempt to manipulate percentiles or leaderboards;
• use automated systems to access the service at scale.

4. Free and paid tiers

Free, permanently:

• the daily puzzle, its result grid, sharing and percentile;
• the streak, including one free freeze per calendar month;
• unlimited Sprint and Zen practice at a fixed difficulty;
• first-wave review of mistakes within a session;
• basic statistics.

Premium adds:

• adaptive difficulty that follows your rating in every mode;
• the spaced review queue, returning error patterns after 1, 3, 7 and 21 days;
• the Skill, Money, True/False and Missing-operand modes;
• your full speed history and skill map;
• unlimited streak freezes.

We may add, change or withdraw features. If a change materially reduces what an active subscription provides, we will tell you in advance and you may cancel.

5. Subscriptions, billing and renewal

Premium is offered as a weekly subscription with a three-day free trial, and as a yearly subscription. Prices are shown in the app in your local currency before you confirm, and may vary by country.

• Payment is charged to your Apple ID or Google account at confirmation of purchase.
• Renewal is automatic unless auto-renew is turned off at least 24 hours before the end of the current period. Your account is charged for renewal within 24 hours before the period ends.
• Free trial. If you take the trial, it converts to a paid subscription unless you cancel at least 24 hours before it ends. We send a reminder before that happens. Any unused portion of a trial is forfeited when you buy a subscription.
• Cancelling is done in your App Store or Google Play account settings — we cannot cancel a store subscription for you. There is a direct link in the app's settings.
• Price changes take effect only after we notify you, and you may cancel before they apply.

Cancelling stops future charges; it does not shorten the period you have already paid for. Premium remains active until the end of that period. For refunds, see the refund policy.

6. What we promise, and what we don't

Sums helps you become faster and more accurate at mental arithmetic through practice. That is the only claim we make, and it is measurable inside the app.

We make no claims about memory, IQ, attention, cognitive function, brain health, academic or professional performance. Sums is not a medical, diagnostic or educational-certification product, and results differ from person to person.

7. Your content and the daily

Puzzles, the generator, the design and the brand are ours or our licensors'. Sharing your daily result grid is encouraged and requires no permission. You may not republish the app's puzzle sets as your own product.

8. Service availability

The app works offline: puzzles are generated on your device. Online features — percentiles, subscription checks, configuration — depend on third-party infrastructure and may be unavailable at times. We provide the service "as is" and "as available", without warranties of uninterrupted or error-free operation, to the extent permitted by law.

9. Limitation of liability

To the fullest extent permitted by law, we are not liable for indirect, incidental or consequential damages, or for lost data, profits or opportunities. Our total liability for any claim is limited to the amount you paid us in the twelve months before the claim arose.

Nothing here excludes liability that cannot be excluded by law, including your statutory consumer rights.

10. Termination

You may stop using Sums at any time by deleting the app. We may suspend or terminate access if you breach these terms, in particular by manipulating results or attacking the service. On termination, sections 6 through 11 survive.

11. Governing law

These terms are governed by the laws of the Republic of Serbia, without regard to conflict-of-law rules. If you are a consumer in the EEA or the UK, you keep the protection of the mandatory laws of your country of residence, and you may bring proceedings in your local courts.

12. Apple and Google

Apple and Google are not parties to these terms and have no responsibility for the app. They are third-party beneficiaries entitled to enforce these terms against you. Any store-specific rules apply in addition to these terms.

13. Changes

We may update these terms. Material changes will be announced in the app before they take effect. Continuing to use Sums after that means you accept the new version.

14. Contact

support@sums.day — Gleb Matsko, individual developer, Serbia.