How much can I overpay on my UK mortgage without a penalty?

Most UK fixed-rate mortgages allow you to overpay up to 10% of your outstanding balance each year without triggering an Early Repayment Charge. On a £200,000 balance that is £20,000 per year. Tracker and variable rate mortgages typically have no ERC at all and allow unlimited overpayment.

Is it better to overpay monthly or make a lump sum?

A lump sum reduces your principal immediately so all future months accrue less interest from that point, generally saving more total interest. Monthly overpayments are easier to manage within the 10% annual allowance and offer more flexibility. Always check your ERC allowance before making a large overpayment.

How does an offset mortgage work compared to overpaying?

An offset mortgage links your savings to your mortgage balance and you pay interest only on the difference. Your savings remain accessible at any time. An overpayment permanently reduces the balance and cannot easily be retrieved. Offset mortgages suit those needing a financial buffer while reducing interest; overpayments suit those committed to reducing debt. Offset rates are typically 0.1-0.3% higher than standard deals.

UK Mortgage Overpayment Calculator

Q: What is an Early Repayment Charge on a UK mortgage?

An Early Repayment Charge (ERC) is a penalty applied when you repay more than your permitted annual allowance during a fixed or discounted rate period. ERCs are typically 1-5% of the excess amount, declining over the fixed period. For example a 2% ERC on £10,000 of excess overpayment costs £200.

Q: Does overpaying my mortgage give a better return than savings?

Overpaying gives a guaranteed tax-free return equal to your mortgage rate. Savings account interest is taxable so a 4.5% savings rate at 20% income tax yields only 3.6% after tax. ISA savings are also tax-free and should be compared directly to your mortgage rate. The comparison depends on your tax rate and the best savings rate available to you.

Calculate how much interest you save and time you cut by making overpayments on your UK mortgage. Includes the 10% annual ERC-free allowance check, Early Repayment Charge cost analysis, lump sum vs monthly comparison, offset mortgage vs overpaying, and tax-free return versus savings account comparison.

Mortgage Balance

Interest Rate

Remaining Term (years)

Monthly Overpayment

Annual Overpayment Allowance (%)

Total Interest Saved

£37,326

Overpayment within 10% allowance: Yes — no ERC risk

Time Saved

6 yrs

New Payoff Date

May 2042

Annual Allowance (10%)

£22,000/yr

Monthly Allowance Equivalent

£1,833/mo

Advanced

Advanced Analysis

10% rule explained, ERC penalties, lump sum vs monthly comparison

Most UK fixed-rate mortgages permit overpayments of up to 10% of the outstanding balance per year without triggering an Early Repayment Charge. This resets each calendar year.

Current Balance

£220,000

Outstanding mortgage

Annual Allowance (10%)

£22,000

Maximum without ERC

Monthly Equivalent

£1,833/mo

Spread over 12 months

Your Annual Overpayment

£3,600

Within allowance

Monthly Overpayment	Annual Total	Within 10% Limit?	Interest Saved	Time Saved
£100/mo	£1,200	Yes	£16,127	2yr 6mo
£200/mo	£2,400	Yes	£27,655	4yr 5mo
£300/mo	£3,600	Yes	£37,326	6yr
£500/mo	£6,000	Yes	£51,739	8yr 5mo
£750/mo	£9,000	Yes	£64,910	10yr 7mo
£1,000/mo	£12,000	Yes	£74,411	12yr 2mo

Pro

Professional Simulator

Offset vs overpay, fixed vs tracker analysis, tax-free return comparison

An offset mortgage links your savings account to your mortgage. Your savings reduce the balance you pay interest on — but you keep access to the money at any time.

Feature	Offset Mortgage	Standard + Overpay
Interest savings	Savings balance offsets daily	Overpayment reduces balance permanently
Access to money	Yes — withdraw savings anytime	No — cannot easily retrieve overpayments
Interest on savings	Effectively earns mortgage rate (tax-free)	Savings earn bank rate (taxable)
ERC implications	None — savings just sit in linked account	Overpayments beyond 10% may trigger ERC
Mortgage rate	Typically 0.1–0.3% higher than standard	Standard market rate
Best for	Self-employed, variable income, emergency fund	Disciplined savers, stable income

Offset example: £220,000 mortgage, £40,000 savings linked. You pay interest on only £180,000. At 4.5%, this saves around £1,800 per year in interest while keeping full access to your £40,000.

How to Use This UK Mortgage Overpayment Calculator

Enter your current mortgage balance, interest rate, remaining term, and the monthly overpayment amount you plan to make. Set your annual allowance percentage — this is usually 10% for UK fixed-rate mortgages. The calculator shows interest saved, time saved, and whether your overpayment stays within the Early Repayment Charge-free limit.

What is a Mortgage Overpayment?

A mortgage overpayment is any amount you pay above your required monthly payment. Extra payments reduce the outstanding principal, which means less interest accrues each month. Over time, overpayments can save tens of thousands in interest and cut years off your mortgage term.

The UK 10% Annual Overpayment Rule

Annual overpayment allowance = 10% of outstanding balance

Example: £200,000 balance
Annual limit = £20,000 (£1,667/month)

If you overpay more than this on a fixed-rate deal:
→ Early Repayment Charge (ERC) applies to the excess
→ Typical ERC: 1–5% of the excess amount

Tracker and variable rate mortgages: usually no ERC at all

The 10% limit resets each year based on the balance at the start of that year (or on your deal anniversary — check your mortgage terms). Unused allowance does not carry forward to the next year.

Offset Mortgages vs Overpaying

An offset mortgage links your savings account to your mortgage. Your savings reduce the balance on which interest is calculated — but unlike an overpayment, you retain full access to your savings at any time.

Offset: £220,000 mortgage, £40,000 savings = interest calculated on £180,000. Savings can be withdrawn any time.
Overpay: Reduce the balance permanently. Cannot retrieve overpayments easily. No ERC within 10% annual limit.
Rate: Offset mortgages typically charge 0.1–0.3% more than equivalent standard deals, but the saving on interest can more than compensate.

Offset mortgages are particularly beneficial for self-employed people or those with irregular income who need a financial buffer but want to reduce interest costs.

Example: Overpaying £300/Month

Sophie overpays her London flat mortgage

Sophie has a £220,000 mortgage at 4.5% with 22 years remaining. She decides to overpay £300 per month.

Mortgage Balance	£220,000
Rate	4.5%
Normal Monthly Payment	£1,333/month
Overpayment	£300/month
Annual Allowance (10%)	£22,000/yr = £1,833/mo
Within ERC-free limit?	Yes — £3,600/yr vs £22,000 limit
Interest Saved	£27,840
Time Saved	5 years 4 months

By paying an extra £300 per month, Sophie pays off her mortgage over 5 years early and saves nearly £28,000 in interest.

Frequently Asked Questions

Most UK fixed-rate and tracker mortgages allow you to overpay up to 10% of your outstanding balance each year without triggering an Early Repayment Charge. For example, on a £200,000 balance that is £20,000 per year or £1,667 per month. Check your mortgage terms as some lenders have different limits or calculate the allowance differently. Tracker and variable rate mortgages typically have no ERC at all.

An Early Repayment Charge (ERC) is a penalty your lender charges when you repay more than your permitted allowance during a fixed or discounted rate period. ERCs are typically 1–5% of the excess amount overpaid, declining over the fixed period. For example, a 2% ERC on £10,000 of excess overpayment costs £200. ERCs compensate the lender for the interest they would otherwise have earned.

A lump sum overpayment reduces your principal immediately, so all future months accrue less interest from that point. A monthly increase applies more gradually. If you have a large sum available, a lump sum generally saves more interest in total — but check your 10% annual allowance first. Monthly overpayments are easier to sustain within the allowance and offer flexibility to stop if your circumstances change.

An offset mortgage links your savings to your mortgage balance. You pay interest only on the difference, but your savings remain accessible. An overpayment permanently reduces the balance and cannot be easily retrieved. Offset mortgages suit those who need a financial buffer; overpayments suit those who want to commit fully to reducing debt. Offset mortgage rates are typically 0.1–0.3% higher, but savings on interest can offset this.

Overpaying your mortgage gives a guaranteed, tax-free return equal to your mortgage rate. Savings account interest is taxable (though the Personal Savings Allowance covers £500/year for basic rate and £250 for higher rate taxpayers). If your mortgage rate is 4.5%, overpaying gives a 4.5% guaranteed tax-free return. A savings account earning 4.5% at 20% tax yields only 3.6% after tax. ISA savings are also tax-free and should be compared directly to your mortgage rate.