A tracker mortgage is a type of variable-rate mortgage. Its interest rate ‘tracks’ (moves in relation to) an external interest rate, normally the Bank of England Base Rate. For example, if the base rate increased by 1% your mortgage rate would also increase by 1%, meaning your monthly mortgage payments would also increase. Tracker mortgages are normally cheaper than fixed rate mortgages, but do carry more risk as they can go up, as well as down.