Should You Overpay Your Mortgage or Save the Extra Cash Instead?

With mortgage rates and savings rates both having moved considerably over the past few years, the old rule of thumb - ‘overpaying your mortgage is basically guaranteed savings’ - deserves a genuine recalculation rather than being taken on faith. Here’s how to actually compare the two. (If you’re still working towards your first mortgage rather than overpaying an existing one, our guide to saving a deposit faster while renting covers that earlier stage instead.)

The core comparison

Overpaying your mortgage effectively earns you a guaranteed return equal to your mortgage interest rate, since every pound you overpay is a pound you’re no longer paying interest on. Saving the same money instead earns you whatever your savings account or Cash ISA pays. The comparison is simple in principle: whichever rate is higher generally wins, all else being equal.

The current rate backdrop

As of mid-2026, average fixed mortgage rates have moved with the Bank of England base rate (held at 3.75% since December 2025), while top savings rates - particularly 1-year fixed Cash ISAs around 4.41% as of May 2026 - have in some cases run close to, or above, typical mortgage rates. This is a meaningfully different picture from the very low interest rate years of 2015–2021, when mortgage rates comfortably exceeded savings rates and overpaying was the clearer winner.

Why it’s not purely about the headline rates

• Tax matters for savings, not for mortgage overpayments. Mortgage interest saved is effectively tax-free (there’s no tax on interest you don’t pay), whereas savings interest may be taxed above your Personal Savings Allowance (see our dedicated article on this) - making the true rate comparison more nuanced than the headline numbers suggest, especially for higher-rate taxpayers.
• Overpayment limits. Most mortgage deals cap penalty-free overpayments at around 10% of the outstanding balance per year - overpay beyond this during a fixed term and you may face an early repayment charge, unlike unlimited flexibility in a savings account.
• Overpaying reduces future flexibility. Once money is used to overpay a mortgage, it’s generally not accessible again without a further advance or remortgage, unlike money kept in savings, which remains available for emergencies or other opportunities.

When overpaying tends to win

• Your mortgage rate is clearly higher than the best available savings rate, particularly relevant for anyone on a higher standard variable rate or an older, less competitive fixed deal.
• You’ve already built a solid emergency fund (see our dedicated article on sizing this) and have no more pressing need for accessible cash.
• You value the psychological benefit of a shrinking mortgage balance, which some people find motivating in a way a growing savings balance doesn’t quite match.

When saving instead tends to win

• Your mortgage rate is lower than achievable savings rates, which has been genuinely possible at points during 2026 for savers able to access the best fixed-rate Cash ISA deals.
• You haven’t yet built an adequate emergency fund - locking money into your mortgage before securing accessible savings is generally the wrong order of priorities.
• You have higher-priority uses for the money, such as maximising an employer pension match (a guaranteed, typically higher return than either option) or clearing more expensive debt like credit cards.

A worked example

Say your mortgage rate is 4.5% and the best available 1-year fixed Cash ISA pays 4.4%. The two are close enough that other factors - your tax band, whether you’ve built an emergency fund, your overpayment allowance, and how much you value flexibility - should probably decide it, rather than the small rate gap alone.

The bottom line

The gap between mortgage rates and top savings rates has narrowed considerably compared with a few years ago, which means this decision deserves a fresh look rather than defaulting to the old assumption that overpaying always wins. Compare your actual mortgage rate against genuinely available savings rates, factor in tax and flexibility, and make sure your emergency fund and any employer pension match are already sorted first.