Last updated: August 29, 2026
Blitzcalc ("the app") is a mental-math practice app for iOS, published by Lars Haneveld. This policy explains what happens to your data when you use it.
Blitzcalc does not collect, transmit, or sell any of your personal data. There is no account, no sign-in, and no server of ours. Everything the app knows about your progress stays on your device — and, if you leave iCloud sync on, in your own iCloud account, which we cannot read.
Blitzcalc stores the following on your device — in Apple's standard preference store (UserDefaults) and in files inside the app's own container:
None of it is sent to us, to any server we operate, or to any third party. The app has no backend and no analytics, and makes no network requests to collect usage data. Deleting the app removes everything stored on the device; see iCloud sync below for the copy iCloud may hold.
If you are signed in to iCloud, Blitzcalc keeps a copy of your progress in your own iCloud account, so it survives a new phone and stays in step across your devices. This uses Apple's iCloud key-value storage. The data goes to your private iCloud — not to us. We have no server and no way to read it.
What syncs: your skill levels, statistics, streaks, badges, review sets, master-class progress, the topics you have chosen to skip, and the first name and starting-point answers you gave during onboarding. Your answer-by-answer history stays on the device.
Sync is on by default when you are signed in to iCloud, and you can turn it off at any time in Settings ▸ iCloud sync. Turning it off stops any further syncing, and leaves the copy iCloud already holds in place — deleting the app does not remove it either, which is exactly why a new phone finds your progress waiting. Turning sync back on restores from that copy. If you want that copy cleared, write to [email protected] and it will be sorted out with you.
Apple's handling of iCloud data is governed by Apple's Privacy Policy.
Blitzcalc can turn one of your review sets into a short code beginning FCSET1-, which you can send to someone else however you like. The code travels through whichever app you choose to send it with — it does not pass through us. It contains only the set's own contents: which skills it covers, its target date, and its name. It carries no personal information and no statistics.