Is an offset mortgage worth it?

An offset mortgage links a savings account to your mortgage. The balance in the savings account is 'offset' against your mortgage balance for interest calculation purposes. For example, if you have a £200,000 mortgage and £30,000 in your offset account, you only pay interest on £170,000. The money in the offset account remains yours — you can withdraw it at any time.

You tell us your mortgage details and how much spare cash you have. We compare two scenarios: (A) putting the money in your offset account to reduce the mortgage interest you pay, versus (B) depositing it into savings accounts and earning interest. We factor in your tax band, Personal Savings Allowance, ISA tax-free status, and any offset limits your lender sets.

It depends on your savings rate versus your mortgage rate, and your tax position. The interest saving from offsetting is effectively tax-free, making it particularly attractive for higher-rate taxpayers. If your savings rates (after tax) are lower than your mortgage rate, offsetting is usually better. This calculator gives you a personalised answer.

The key advantage of offsetting over overpaying is accessibility. With an offset, your money stays in a savings account that you can withdraw from at any time. With overpayments, your money goes directly into the mortgage and typically can't be accessed without remortgaging. Both save the same amount of interest, but offset gives you more flexibility.

Yes. Money in your offset account remains accessible. You can withdraw it whenever you need it, though doing so will increase the amount of mortgage interest you pay (since less is being offset). This is one of the main advantages over making overpayments.

Some lenders cap the amount you can hold in your offset account. For example, a lender might limit offset savings to £50,000 or to 100% of the mortgage balance. Any money above this limit sits in the account but doesn't reduce your mortgage interest. Check your mortgage terms for any offset cap.

Offsetting is effectively tax-free — you don't earn interest, you avoid paying it, so there's nothing to tax. Savings interest outside ISAs is taxable above your Personal Savings Allowance (£1,000 for basic rate, £500 for higher rate, £0 for additional rate). This makes offsetting more attractive for higher-rate taxpayers.

Yes, offset mortgages can be particularly beneficial for higher-rate taxpayers. Since the interest saving from offsetting is tax-free, while savings interest is taxed at 40% above a smaller £500 allowance, the effective return from offsetting often beats taxable savings. This calculator accounts for your specific tax position.

When your offset mortgage deal ends, you'll typically move to your lender's Standard Variable Rate (SVR). Your offset account will continue to work the same way, but at the new rate. This is a good time to review whether to remortgage to a new offset deal or switch to a standard mortgage and move your savings elsewhere.

It depends on the rates. ISA interest is tax-free, just like the offset saving. If your ISA rate equals your mortgage rate, they're mathematically identical. If your ISA rate is higher, save in the ISA. If lower, offset wins. The main practical difference is that offset savings reduce your mortgage immediately and are always accessible, while ISAs have annual contribution limits.