How an offset mortgage works
With a standard mortgage, you pay interest on the full outstanding balance every month. An offset mortgage changes this by "offsetting" your savings (and sometimes your current account balance) against the mortgage debt. The lender calculates interest daily on the mortgage balance minus your offset savings, so the more you have in savings, the less interest you pay. Your savings are not used to pay down the loan — they remain yours and you can usually withdraw them at any time — but while they sit in the offset account, they effectively earn the mortgage rate of interest, completely tax-free.
Your savings are not used to pay down the mortgage — they remain yours and you can usually withdraw them at any time. But while they sit in the offset account, they effectively "earn" the mortgage rate of interest, tax-free. This can be particularly valuable for higher-rate and additional-rate taxpayers, who would otherwise lose 40% or 45% of their savings interest to tax.
There are two main types: a savings offset, where a separate savings account is linked to the mortgage, and a current account offset (sometimes called an "all-in-one" or "current account mortgage"), where your salary goes into the mortgage account and you spend from it — every pound in the account reduces your interest that day.
Pros and cons
| Advantages | Disadvantages |
|---|---|
| Pay less interest — savings reduce the balance you are charged on | Offset rates are typically 0.25–0.75% higher than standard fixed rates | Savings stay accessible — you can withdraw them when needed | Your savings earn no interest (they save interest instead) | Tax-efficient — the "return" is the mortgage rate, paid tax-free | Fewer lenders and products to choose from | Flexible overpayments — some let you draw back overpayments later | May require you to hold a current account with the lender | Good for fluctuating income — self-employed can park lump sums temporarily | Small savings balances may not justify the higher rate |
MoneyHelper — Offset mortgages · accessed 2026
Offset mortgage vs a regular mortgage plus savings
The key question is whether the interest you save by offsetting outweighs the higher rate you typically pay on an offset mortgage. Suppose you have a £200,000 mortgage and £30,000 in savings. A standard two-year fix costs 4.75%, while an offset deal costs 5.25%.
With the standard mortgage, you pay £200,000 × 4.75% = £9,500 interest per year. Your £30,000 in a savings account at 4% earns £1,200 gross — but as a 40% taxpayer you keep only £720. Net cost: £9,500 − £720 = £8,780.
With the offset mortgage, you pay interest on £170,000 at 5.25% = £8,925 per year, and your savings earn nothing but are not taxed. Net cost: £8,925. In this example the standard mortgage is slightly cheaper — but if your savings were £50,000, the offset would cost £150,000 × 5.25% = £7,875, comfortably beating the standard deal. The bigger your savings buffer, the more an offset mortgage makes sense.
Who is an offset mortgage best for?
Offset mortgages tend to suit three groups. First, higher-rate taxpayers with meaningful savings: because the offset return is tax-free, it beats a taxable savings account for anyone paying 40% or 45% tax. Second, self-employed people or those with irregular income: you can park lump sums (like a tax provision) in the offset account to reduce interest, then withdraw them when the tax bill is due. Third, people who want flexibility: if you may need access to a large cash buffer but also want to reduce your mortgage interest, an offset avoids the commitment of a permanent overpayment.
They are less suitable if you have only a small amount of savings (the higher rate will outweigh the offset benefit), or if you prefer the certainty of the lowest possible fixed rate and are happy to lock savings away in an ISA or fixed-term bond.
Worked example: £200,000 mortgage, £30,000 savings
| Standard mortgage (4.75%) | Offset mortgage (5.25%) | |
|---|---|---|
| Mortgage balance | £200,000 | £200,000 |
| Offset savings | — | £30,000 |
| Balance charged interest on | £200,000 | £170,000 |
| Annual interest | £9,500 | £8,925 |
| Savings interest (4% gross, 40% taxpayer) | £720 net | £0 |
| Net annual cost | £8,780 | £8,925 |
In this scenario the standard mortgage edges ahead by £145 a year. But increase the savings to £50,000 and the offset wins by £905 a year — because the interest saved on a larger offset balance more than compensates for the higher rate. Use our mortgage calculator to model your own numbers, and our overpayment calculator to compare offsetting against permanent overpayments.
Frequently asked questions
Do I lose access to my savings with an offset mortgage?
Is an offset mortgage tax-free?
How much do I need in savings for an offset mortgage to be worth it?
Can I overpay an offset mortgage?
Are offset mortgages only for people with big savings?
Sources
- MoneyHelper — Offset mortgages (how they work, pros and cons, accessed 2026)
- MoneyHelper — Types of mortgage (offset vs other mortgage types, accessed 2026)