Mortgage rates change with Bank of England base rate. When rates drop significantly and you're approaching end of fixed term, refinancing (remortgaging) can save substantial money over the next fixed period.
When to consider
End of current fixed term within 6 months. Base rate drops 0.5%+ from your current rate. Property value increased significantly (LTV better band). Income increased significantly.
How to do it
Compare rates 3-6 months before current deal ends (don't wait until standard variable rate kicks in). Use broker (free for most domestic mortgages) or compare directly via MoneySavingExpert, Habito. Fixed vs tracker decision depends on rate outlook.
Refinancing one mortgage from 4.5% to 3.5% on £250k saves roughly £200/month — £2,400/year. Worth the few hours of paperwork.