What spends a credit
Only two things spend a credit: a concierge chat response, and adjusting a single day of your itinerary. A Concierge question with a photo attached uses 2 credits (reading the photo is part of the answer). You always act first, a credit is never spent by merely opening a page.
What's always free
Opening the map, re-reading past answers, locking and reordering itinerary days, checking your balance, and browsing everything you've already built. If a question is out of scope (anything that isn't Italy travel) you get a short note back and no credit is spent.
Your allowance
Trip Pass includes 200 credits; Italy Year includes 600 credits during your 12-month access period. Your current balance shows in the Concierge's context strip and on your Account page.
Running low
Top-ups start at €9 and need an active pass, see the top-ups article. Top-up credits are added to your balance, they never replace it.
When your access ends
Your credit balance is kept exactly as it was, but it's only usable with an active pass. Buying again while your access is still live stacks the new allowance on top; buying again once access has ended re-seeds the allowance for the new term, so it's best to use top-up credits within the term you bought them in.