With any loan, there are two parts. The amount you borrowed and need to repay (the ‘principal’), and interest on top of that.
With Bounce Back Loan repayments your principal repayments will stay the same every month (unless you take a Pay As You Grow payment holiday).
We calculate interest each month, based on the amount of principal that’s outstanding (that you haven’t paid back yet). As you repay more of the principal over time, your interest payments go down.