Buying a Property

The 10% Annual Mortgage Overpayment Limit — What It Means and How to Plan Around It

Most fixed-rate mortgages allow penalty-free overpayments of up to 10% of the outstanding balance per year. This guide explains how the limit works, what happens if you exceed it, and strategies to maximise overpayment within the rules.

Published: 1 Jan 2026 · Updated: 1 Mar 2026 · 7 min read

Why Lenders Cap Overpayments

When a lender advances money on a fixed-rate mortgage, they typically fund that lending by borrowing at a fixed rate themselves in the wholesale money markets. If you repay the mortgage early or make large overpayments, the lender is stuck holding the more expensive funding without the loan income it was expected to cover.

The Early Repayment Charge (ERC) is the mechanism by which lenders recover this cost. The 10% annual overpayment allowance is the concession most lenders build into their fixed-rate products — allowing borrowers to make meaningful overpayments without triggering an ERC.

Use our [mortgage overpayment calculator](/mortgage-overpayment-calculator) to model your overpayment strategy within your annual allowance.

How the 10% Limit Is Calculated

The allowance is almost universally calculated on the **outstanding balance at the start of each year of the mortgage**, not the original loan amount. This distinction matters as your balance reduces over time.

**Example:**

Original mortgage: £250,000
Balance at start of year 3 of fixed deal: £238,000
10% allowance: £23,800

In year 4:

Balance at start of year 4: £215,200 (after year 3 normal payments plus £23,800 overpayment)
10% allowance: £21,520

Each year's allowance is based on the balance remaining, not the starting loan.

What Counts as an Overpayment?

Only payments **above and beyond your contractual monthly payment** count toward the 10% overpayment limit. Your standard monthly payment does not consume any of your allowance.

So if your monthly payment is £1,100 and you pay £1,400, the £300 extra per month counts as overpayment. Over 12 months that is £3,600 — modest relative to a £200,000 balance (1.8%), well within the 10% limit.

Most lenders measure the allowance over the mortgage year (12 months from the start of the fixed term, or the anniversary of the mortgage), not the calendar year. Check your mortgage offer letter for the specific definition.

What Happens If You Exceed the Limit?

Exceeding the 10% limit triggers an Early Repayment Charge on the excess portion. ERCs are typically structured as:

Year of fixed term	Typical ERC
Year 1	5% of excess
Year 2	4% of excess
Year 3	3% of excess
Year 4	2% of excess
Year 5	1% of excess

On a five-year fix, the ERC reduces to 1% in the final year. Tracker and variable rate mortgages usually have no ERC at all, and their overpayment limits are either absent or much higher.

**Example of ERC calculation:**

You want to overpay £30,000 in year 2 of a five-year fix
Your balance at the start of the year: £200,000
Your 10% allowance: £20,000
Excess: £10,000
ERC rate (year 2): 4%
ERC charge: £400

In this case, you could overpay £20,000 penalty-free. The additional £10,000 would cost £400 in charges. Whether that is worth it depends on the interest saving generated by the extra £10,000 — for most borrowers with rates above 4%, it typically is.

Strategies to Maximise Penalty-Free Overpayment

**Split the overpayment across two mortgage years:** If your allowance is about to reset, you can make one overpayment in the final weeks of the current mortgage year (up to the remaining allowance) and another immediately after the anniversary when the new year's allowance opens.

**Stagger a windfall over two years:** If you receive a large inheritance in November, you might immediately pay up to the current year's remaining allowance, then schedule the rest for January when the new year's allowance opens.

**Track your running total:** Keep a note of all overpayments made in the current mortgage year. It is easy to lose track of ad-hoc extra payments made over time.

**Review at product expiry:** When your fixed-rate deal ends and you remortgage, there is typically a short window during which no ERC applies. This is the opportunity to make large overpayments — up to and including full repayment — without any charges.

Products with Higher or No Limits

Not all fixed-rate mortgages cap at 10%. Some lenders offer:

**Flexible mortgages** — allow unlimited overpayment, often at a slight rate premium
**Offset mortgages** — link savings to the mortgage balance; interest is charged only on the net balance; effectively unlimited "virtual" overpayment
**Tracker mortgages** — most have no ERC at all, so unlimited overpayments are possible without penalty

If you anticipate making large overpayments (for example, if you expect a significant bonus each year), it may be worth choosing a product with a more generous overpayment allowance even if the rate is marginally higher. Run the numbers — the rate premium on a flexible product versus the ERC you would otherwise pay can make the flexible deal cheaper overall.

Checking Your Specific Terms

The 10% figure is standard but not universal. Always verify by:

Checking your original mortgage offer document (the binding terms)
Logging into your lender's online portal (most show the remaining allowance for the current year)
Calling your lender's mortgage servicing team

Our [mortgage overpayment calculator](/mortgage-overpayment-calculator) helps you model the interest savings from staying within your penalty-free limit — so you can plan confidently and maximise the benefit without incurring unnecessary charges.