Should I overpay my mortgage or put money in savings in 2026?

In April 2026, with best-buy 5-year mortgage fixes around 5.20% and top 1-year fixed savings at roughly 4.7% gross, overpaying your mortgage usually wins mathematically for higher-rate taxpayers (net savings return of about 2.82% after 40% tax). Basic-rate savers who can use a cash ISA at 4.5% tax-free may break even or marginally beat overpaying. Whichever you pick, hold a 3-6 month emergency fund in easy access before you commit — that’s the sacred baseline.

The one-line rule

Compare your net-of-tax savings rate to your mortgage rate. If savings (after tax) pay less than the mortgage costs, overpay. If savings (after tax) pay more, save.

In April 2026 that cashes out roughly like this:

Taxpayer status	Best 1-yr fix savings	Net rate (after tax)	Mortgage rate 5.20%	Winner
Cash ISA (any taxpayer)	4.50%	4.50%	5.20%	Overpay
Basic rate, PSA not used	4.70%	4.70%	5.20%	Overpay
Basic rate, PSA exhausted	4.70%	3.76%	5.20%	Overpay
Higher rate, PSA not used	4.70%	4.70%	5.20%	Overpay
Higher rate, PSA exhausted	4.70%	2.82%	5.20%	Overpay clearly
Additional rate	4.70%	2.59%	5.20%	Overpay clearly

The gap favours overpaying in nearly every case at current 2026 rates. That’s a flip from 2023-2024 when savings briefly beat low inherited fixes at 1.5-2.0%.

Understanding the Personal Savings Allowance

The Personal Savings Allowance (PSA) lets you earn interest tax-free outside an ISA:

Basic-rate taxpayers: £1,000 of interest tax-free
Higher-rate taxpayers: £500 of interest tax-free
Additional-rate: £0

At 4.7% savings rates, a higher-rate taxpayer uses up the £500 PSA on roughly £10,640 of savings. Above that, every extra pound of savings interest is taxed at 40%. A cash ISA (£20,000 annual allowance) sidesteps this entirely — which is why it’s often the best place for pre-mortgage-overpayment cash if you’re a basic-rate taxpayer.

A couple comparing savings interest and mortgage interest on a laptop and notebook — Do the maths post-tax: a higher-rate taxpayer’s 4.70% savings rate becomes 2.82% after 40% tax, losing cleanly to a 5.20% mortgage.

The emergency fund comes first — no exceptions

Before any overpayment, hold 3-6 months of essential outgoings in instant-access savings. Why?

Overpayments are not easy to reverse. Most lenders won’t let you borrow the money back; you’d need a further advance at a higher rate, or another remortgage.
Job loss, illness or a broken boiler can take months to resolve. A cash buffer prevents expensive payday-loan decisions.
An emergency fund also strengthens your credit profile — a real benefit for any future borrowing.

If you have £5,000 to deploy and no emergency fund, the answer is easy: put it in a best-buy easy-access account or cash ISA first, regardless of the tax or rate maths.

A worked example: £10,000 to deploy

Scenario: higher-rate taxpayer, £200,000 mortgage at 5.20% (5-year fix, 22 years left), emergency fund in place, PSA exhausted.

Option A — Overpay £10,000
- Interest saved over the remaining 22 years: roughly £12,100 (assuming rate stays put)
- ERC risk: zero (within 10% annual allowance)
- Liquidity: gone, tied up in the house
Option B — Cash ISA at 4.5% for 5 years
- Interest earned: £2,456 (compounded)
- Tax: £0
- At year 5, £12,456 — but your mortgage has continued to accrue interest at 5.20%
- Net position vs Option A: roughly £1,800 worse after 5 years

Overpaying wins here by about £1,800 over the fix, and the gap widens if you overpay repeatedly. Model your own numbers with our overpayment calculator.

When saving beats overpaying

Two realistic cases for 2026:

Basic-rate taxpayer with spare cash ISA allowance. A 4.5% tax-free cash ISA gets close enough to a 5.20% mortgage that the flexibility of easy access is arguably worth the small difference.
You’ll hit the 10% ERC cap this year. Overpaying above the cap triggers the ERC (typically 3% in year 3 of a 5-year fix). Any extra should sit in savings until January resets the allowance.

Also consider pensions — higher-rate relief on pension contributions often beats either savings or overpayments, particularly if you’re behind on retirement contributions.

The misconception worth clearing up

“Savings rates are higher than my mortgage rate, so saving must win.” Check gross vs net. A best-buy 1-year fix at 4.70% gross is worth only 2.82% after higher-rate tax if you’ve used up your PSA — nowhere near the 5.20% your mortgage costs. Always compare post-tax savings rates with your fixed mortgage rate. The arithmetic changes when rates shift, so redo it at every remortgage — and remember that overpayments beat savings emotionally too, because a shorter mortgage term is a permanent win.

This is information, not regulated advice. For a proper plan that considers pensions, ISAs and overpayments together, speak to an independent financial adviser.