In a stepped certificate, does the monthly payout stay the same?

No. A stepped (declining) certificate has its highest rate in year 1, then a lower rate each year after, so the monthly payout falls with it. The big figure in an ad is usually the year-1 rate only; the whole schedule is what describes the certificate.

Example with a hypothetical 3-year schedule, per 100 pounds: 24% in year 1, 20% in year 2 and 16% in year 3. The monthly payout is 2 pounds in year 1, about 1.67 in year 2 and about 1.33 in year 3, so the last year's payout is two thirds of the first year's.

If you will rely on this income for fixed expenses, plan on each year's payout, not on year 1. And tell stepped from variable: a stepped schedule on a fixed-rate certificate is agreed from day one, while a variable rate moves with a reference rate.

Before buying, ask the bank for the year-by-year rate schedule for the payout frequency you will choose and the amount paid on your sum each year, and check the rate type in the key-facts statement.