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Lump sum mortgage payment calculator
Apply a one-time payment — a bonus, tax refund, or windfall — and see exactly how much interest it saves and how much sooner you're debt-free.
Model a one-time payment
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Estimates only, not a loan offer. Excludes taxes, insurance and fees unless entered. See our disclaimer.
What a one-time payment really does
A single large payment toward principal can save a surprising amount of interest, because it permanently shrinks the balance that interest is charged on for the rest of the loan. To model it above, enter your loan, then type your amount in the one-time extra payment field and choose the payment number to apply it at.
Timing matters most
The same lump sum saves far more early than late. On a typical 30-year mortgage, applying a windfall in the first few years can save several times what it would save near the end — so if you're going to do it, sooner is better.
Lump sum vs recast vs extra monthly
A lump sum shortens the term; a recast lowers the payment; steady extra monthly payments are easier to sustain. Many people combine a one-time payment with a small monthly extra — try both together in the calculator above.
Frequently asked questions
- How do I calculate the effect of a lump sum payment on my mortgage?
- In the calculator above, enter your loan, then put your one-time amount in the "One-time extra payment" field and the payment number to apply it at. The summary instantly shows how much interest you save and how much sooner the loan is paid off.
- Does a lump sum lower my monthly payment?
- No — a lump sum shortens the term and cuts total interest, but your required monthly payment stays the same, unless your lender recasts the loan. A recast re-amortizes the lower balance into a smaller payment over the remaining term.
- When is the best time to make a lump sum payment?
- The earlier in the loan, the bigger the interest savings, because interest is charged on the balance and the balance is highest early on. A lump sum in year 1 saves far more than the same amount in year 20.
- Should I use a windfall on my mortgage?
- It depends on your situation — many people first cover an emergency fund and any higher-interest debt, then weigh a mortgage lump sum against investing. Paying the mortgage is a guaranteed return equal to your rate.