I slightly improved the spreadsheet form from FAQ: Everything you need to know about forum 'activity, account ranks and merit[url] by displaying a "next period" cell so that you don't have to manually go through the list of dates to figure it out. Thought I'd share it here since I'm not sure who owns the original spreadsheet and can't comment on the FAQ post.

https://docs.google.com/spreadsheets/d/1r-FAjQg0r0Is8HqKt0u9R_MHwwlNQhoXCBTBduzxTAE/edit?usp=sharing