How a lump sum helps
A lump sum reduces your balance straight away, so every later payment pays off more capital and less interest. The calculator keeps your normal monthly payment the same and adds your overpayments, so the loan is paid off sooner. It works month by month, charging interest at one twelfth of the annual rate on what you still owe.
Some lenders reduce your monthly payment instead of the term after an overpayment; this calculator shows the effect of keeping the payment the same.
Worked example
On a £200,000 mortgage at 4.5% with 25 years left, a £10,000 lump sum saves £19,300.45 in interest and 2 years 2 months. A £20,000 lump sum saves £35,968.47 and 4 years 2 months.
Check your allowance
Many fixed and discounted deals let you overpay up to 10% of the balance each year without an early repayment charge. Check your mortgage terms first.
What this calculator assumes
The calculator takes your balance and rate, works out the normal monthly payment over the time left, then replays the loan month by month with your overpayments added. A lump sum is taken off the balance at the start, and any monthly extra is added on top.
It leaves out early repayment charges and the lender's annual overpayment allowance, so check your own terms before relying on the saving.
Inputs for the home loan lump sum calculator
Amount you owe
Your current mortgage balance.
Interest rate (per year)
Your current interest rate.
Time left to repay
How many years are left on the loan.
Extra each month
The amount you'll pay on top of your normal payment each month. Enter 0 for none.
One-off lump sum now
A single overpayment made now. Enter 0 for none.
CALCULATOR QUESTIONS
Home loan lump sum calculator questions
How much can I overpay without a penalty?
Many deals allow up to 10% of the balance a year without an early repayment charge. Check your terms.
Will a lump sum lower my payment or shorten my term?
It depends on your lender. This calculator shows the term shortening with the same payment.
How much would £10,000 save?
On £200,000 at 4.5% with 25 years left, £19,300.45 of interest.
Will my lender charge me for overpaying?
It depends on your agreement. Check for early repayment or settlement charges before you overpay.