ServerCrate / Tools / Retention calculator
Set your keep rules and this page runs the same selection restic's forget uses, over years of simulated backups. You get every restore point that survives, how far back you can go, an honest storage estimate, and the exact command to use.
Restic walks your snapshots from newest to oldest. Each rule (--keep-daily, --keep-weekly, --keep-monthly, --keep-yearly) keeps the newest snapshot in each day, week, month or year it has not seen yet, until its count runs out. A snapshot kept by any rule survives. That is why the rules overlap rather than add up: 7 daily and 4 weekly gives you 9 or 10 restore points, not 11, because the newest snapshots of this week and last week satisfy both rules.
Weeks are ISO weeks, Monday to Sunday, so the weekly snapshot you keep is the last one of each week. Monthly keeps the last snapshot of each calendar month, and yearly the last of each year. If backups skip a day, the rule simply moves on to the next day that has one.
Restic stores each unique chunk of data once. Two restore points a day apart share almost everything, so keeping both costs only what changed between them. Restore points a month apart cost up to a month of changes, capped at the full data size. This page adds those gaps up for the snapshots your policy keeps, then applies the compression you picked.
On ServerCrate the key your servers back up with is append-only: it adds snapshots and never deletes them, so ransomware on a machine has nothing to erase. Cleanup runs with a separate cleanup key from your vault page, and every vault also keeps up to 7 days of server-side snapshots that no key can touch. Read the full retention guide or start with a free 10 GB vault.