How is the return on Islamic savings accounts and certificates calculated?

An Islamic bank does not grant a fixed interest rate set in advance at the time of purchase. The money is invested under the Mudaraba formula (a Sharia-compliant profit-sharing partnership), in which the customer is the "capital owner" (rab al-mal) and the bank is the "investment manager" (mudarib).

The actual profits generated by the investment are distributed periodically (monthly or quarterly) at an agreed common ratio (for example 70% for customers and 30% for the bank), and the return is variable: it can go up or down according to the actual profits.