Monthly-payout certificate: what do I receive when it matures?

In a certificate with monthly payout, the return reaches you in instalments throughout the term, so on the day it matures you get your principal back, plus the last payment if it falls on that day, not a large lump of return. What you earned over the whole term is the sum of all the payments.

Hypothetical example per 100 pounds in a certificate of 3 years at a fixed 20%: the monthly payment is about 1.67 pounds, and the 36 payments add up to 60 pounds over the three years. On maturity the 100 comes back with the last payment.

There is also a difference between return paid and return accrued but not yet paid: the return is paid only on the payout dates, so between two payments there is return for the period not yet paid, which is paid on its date; how it accrues within the period follows the product's terms.

If you spend the payments as they arrive, the total will not be sitting there at the end. With a stepped certificate the payment changes each year; with a variable rate the figures are expected at today's rate.

Ask the bank for the payout schedule with its dates and total on your amount, and check the key-facts statement for the day the return starts accruing and the payout dates.