How the allowance is measured
The limit may be based on the balance, the original loan, or a specific period in the mortgage year. That detail changes how much headroom you really have.
Mortgage Overpayment Limits UK: The 10% Rule & ERC Explained
Many borrowers hear about a 10% rule, but the exact allowance and any charge still depend on the mortgage terms.
Direct answer
The 10% rule is a common guide used on some UK mortgages to describe how much you can overpay within a year without a charge. It is not universal, and if you exceed the allowance an early repayment charge may apply, so the exact wording in your own mortgage terms matters more than the rule of thumb.
Key points
- The 10% rule is common, not guaranteed
- ERC means early repayment charge
- Monthly overpayments and lump sums may both count towards the same limit
What should you check?
A few details make the difference between a helpful overpayment and an expensive one.
Whether an ERC applies
Charges are most often relevant during fixed or discounted periods, which is why checking the mortgage deal stage matters.
How lump sums are treated
A one-off payment may count towards the same allowance as regular monthly overpayments, so it is worth checking before you act.
How to test the impact
Once you know the safe allowance, use the mortgage overpayment calculator to estimate what that level of extra payment could change.
Related guides
Use these pages to connect the rule with the practical outcome.
Calm trust note
Rule of thumb does not replace the actual mortgage terms.
This page explains the common idea behind the 10% rule and ERCs, but your own lender wording is the part that counts. Always check the exact allowance before making a larger payment.
Check the likely impact before you overpay
Use the calculator with a realistic extra payment that fits inside your own mortgage allowance.