The interest rate you pay when you borrow money will dictate how much you pay back. Interest rates are generally fixed or variable. As the name suggests a fixed rate will stay the same for a period of time whereas a variable rate can change.
Variable interest rates can change over time because they are based on a benchmark interest rate or index that changes, such as the Bank of England’s base rate. The Bank of England's base rate is the rate the Bank of England charges other banks and other lenders when they borrow money. Benchmark interest rates are regularly updated interest rates that are publicly accessible. They are a useful basis for all kinds of financial contracts such as bank overdrafts and Mortgages. When the variable rates goes up and down it affects how much interest you earn on your savings or pay back on money you have borrowed
Fixed interest rates on loans or savings accounts do not go up and down. A fixed-rate loan has an interest rate that stays the same for an agreed period of time so you pay back the same amount each month. A fixed rate of interest on your savings means that the same rate of interest will be applied to your savings over the agreed period.