Mortgage Overpayment Calculator
Enter your outstanding balance, interest rate, and how much extra you can pay each month. See exactly how many months you cut off and how much total interest you save - with a chart comparing both schedules. Nothing uploaded.
Full amortization schedule
Balance Over Time
Learn more: why an early overpayment beats a late one
Interest is charged on the balance
Each month the tool charges interest of balance times the monthly rate, then puts the rest of your payment, plus any overpayment, against the balance. The balance is largest at the start, so the interest part of each payment is biggest then and shrinks as you pay down. An overpayment cuts the balance from that point on, so the earlier it goes in, the more months of interest it removes.
Take a 200,000 mortgage at 5% over 25 years. The payment is 1,169.18 a month and the total interest is 150,754. A 10,000 lump sum at the start saves 22,885 of interest and 28 months. The same 10,000 paid after 10 years saves 10,421.
Monthly overpayments add up too. An extra 200 a month on that mortgage clears it 74 months early, in 226 months, and saves 41,843 of interest. The tool keeps your monthly payment the same and shortens the term, as it does for a lump sum, which the tool applies at the start.
Lump sum or monthly
A lump sum at the start beats the same money spread over a year, since the balance falls at once. On the example loan, 1,200 paid now saves 2,955, while 100 a month for 12 months saves 2,845. The gap is small, so pick whichever fits your cash flow.
Overpayment limits
Lenders cap penalty-free overpayments. Principality's page on overpaying your mortgage says you can overpay up to 10% of the balance each calendar year without an early repayment charge, and that more than that may trigger one. It also says regular monthly payments do not change when you overpay. The overpayment shortens the term instead.
That is one lender's terms. Others vary by product, so check your offer or ask your lender, and keep your overpayments within the allowance. The tool does not check the limit. It also calculates interest monthly, where a lender may use a different method, so its numbers are close but not exact.
FAQ
Should I overpay or save the money?
That depends on your mortgage rate against what savings earn after tax, and on your need for cash you can reach. Overpaying earns a return equal to the interest you stop paying, but the money is harder to get back out. This is general information, not financial advice.
Does a monthly overpayment beat a lump sum?
Not when the lump sum goes in at the start. In the example, 1,200 up front saved 2,955 while 100 a month for a year saved 2,845. A lump sum later in the loan saves less than the same sum earlier.
Does overpaying lower my monthly payment?
Not in the tool, which keeps the payment and shortens the term. Principality says the same of its mortgage. Some lenders let you recalculate a lower payment, so ask yours.