Hey @juanmaia and welcome to the restic community
From the restic documentation on Removing snapshots according to a policy:
--keep-within duration keep all snapshots which have been made within the duration of the latest snapshot.
duration needs to be a number of years, months, days, and hours, e.g.
2y5m7d3h will keep all snapshots made in the two years, five months, seven days, and three hours before the latest snapshot.
So you can simply keep doing your backups as you would and then once in a while you can run:
restic forget --keep-within 30d and this makes sure that all your snapshots that you have taken, no matter when or how many days you didn’t do any backups, it is always 30 days from now backwards.
Another explanation is:
So if you give a duration of 12m, and your last snapshot was made 1m ago, it will keep all snapshots within 13 months of now. The reason it’s since the latest snapshot is to ensure you have a window of snapshots for that long which you can restore, rather than deleting snapshots over time just because time is passing.
I hope this helps you. If it does, please let us know