Compare offsetting savings against mortgage interest and fees.
Estimate how much mortgage interest an offset account could save, how much sooner the mortgage could be repaid, and whether forgone savings interest or fees change the result.
Useful for cash-rich borrowers
Offset mortgages can reduce interest while keeping savings accessible, but you may give up savings interest or pay fees.
Estimated net benefit
£51,363
After estimated offset fees and savings interest forgone.
Inputs
Offset details
Estimate
Results
Estimated mortgage interest saved
£76,783
Time saved: 4 years 6 months
Offset balance used
£40,000
Standard payment
£1,403
Savings interest lost
£22,960
Offset fees
£2,460
Assumes the same monthly mortgage payment and a constant savings balance in the offset account.
Assumptions
Offset mortgage assumptions
Check these inputs before relying on the result.
- Mortgage balance
- £240,000
- The outstanding balance used in the offset model.
- Interest rate
- 5.00%
- Assumed to stay fixed for the remaining term.
- Remaining term
- 25 years
- Used to estimate the repayment mortgage path.
- Offset savings
- £40,000
- Assumed to stay in the offset account and reduce the balance interest is charged on.
- Savings return assumption
- 3.50% before 20% tax
- Used to estimate savings interest given up by using an offset account.
- Product fees
- £10 monthly offset fee
- Offset fees are included. Other mortgage fees and product restrictions are not personalised.
Last reviewed
12 June 2026
Interest method
Monthly interest is estimated from the annual rate unless a page states a different method. Lender figures can use daily interest, product-specific rules, and exact payment dates.
Educational scope
UK-focused calculator estimate. It explains trade-offs and does not make a personal recommendation.
How this is calculated
- The annual interest rate is converted into a monthly rate.
- Each month, interest is estimated on the current mortgage balance.
- The repayment first covers that month's interest. The rest reduces the balance.
- As the balance falls, less interest is charged and more of each payment goes towards the debt.
Main limitations
- The estimate uses the values entered on this page and does not check lender eligibility, affordability, credit history, product availability, or personal tax treatment.
- Fees, ERCs, insurance, valuation costs, legal costs, rate changes, and overpayment rules are included only where the calculator explicitly asks for them.
How offset savings are treated
- The calculator estimates the standard repayment mortgage path.
- It then reduces the interest-bearing balance by the savings held in the offset account.
- It estimates the mortgage interest saved, offset fees paid, and savings interest given up.
- The net benefit compares the mortgage saving with those offset costs.
Results are estimates based on the assumptions shown here. They are not financial advice and can differ from lender figures because real products, fees, rate changes, overpayment rules, and repayment timing vary.
Trade-off
What the offset is really worth
Net benefit
£51,363
Monthly benefit
£209
Offset term
20 years 6 months
Before choosing offset
Check the details
Compare the offset mortgage rate against standard mortgage deals.
Check whether your savings could earn more after tax elsewhere.
Confirm fees, minimum savings requirements, and how quickly savings can be withdrawn.
Important disclaimer
This calculator provides estimates only and does not constitute financial advice. Offset mortgage products, rates, fees, savings access, tax treatment, and repayment rules vary by lender and by personal circumstances.