When you create an exchange, you he 90 days for that trade to count towards your Loyalty Program level. On the 91st day, that initial trade doesn't count anymore, and the period moves forward to include your new trades. Think of it like a moving window that always covers the last 90 days.
In your Customer Account, you can find a chart that shows which trades are currently inside this 90-day window and which ones are not. If you’ve accumulated enough, you will move up a loyalty level. Check out the requirements here. You will keep the level indefinitely, even if you swap less in the future.
Let's look at the example of John. John signed up with SimpleSwap and his first exchange accounted for 0.1 BTC. He received 0.05% cashback thanks to the Bronze level he received automatically. Two months later, he traded the same amount (0.1 BTC), so now his total is 0.2 BTC within a 90-day window.
When he came back another two months later, the first trade was not within the 90-day period, but the second trade was. John's third exchange amounted to 0.2 BTC, so his total within the 90-day window became 0.3 BTC (0.1 BTC from the second trade plus 0.2 BTC from the third). This means that John received the Silver level, and from now on he'll be getting 0.1% BTC cashback for every exchange until he reaches the next level.