Homeowners can save on average £4,500 a year by switching from their lender's standard variable rate (SVR), according to analysis from online mortgage broker Trussle.
Trussle's calculation was based on the average UK house price of £230,630 with a 60 per cent loan-to-value (LTV) mortgage (£138,378).
The savings were identified by Trussle by subtracting annual repayments from average two-year fixed rate deals (£2,393.94) from average annual SVR repayments (£6,957.39).
The "whole of market" data was collated on February 26.
Ishaan Malhi, chief executive and founder of Trussle, said: "Millions of homeowners are collectively missing out on billions of pounds as a result of switching inertia.
"Breaking down the figures shows just how beneficial it can be to move away from a lender's SVR. Switching mortgages is not yet clear or simple. This is a critical issue for homeowners and is costing them a huge amount of money and stress."