Lump-Sum Extra Payment Calculator
How a single one-time extra payment shortens a loan and cuts total interest.
Every calculation runs locally in your browser. Nothing you enter here is sent to a server or stored anywhere.
Monthly payment
$1,896
Months saved
58 months
Interest without lump sum
$382,633
Interest saved
$91,623
For informational and educational purposes only — not financial, investment, or tax advice, and not a substitute for consulting a qualified professional about your specific situation. TrueMeasureKit is not liable for decisions made based on these results. See our Terms of Service.
One extra payment early beats the same amount late
A lump-sum payment goes entirely to principal, and every dollar off the principal stops accruing interest for the rest of the loan — so the earlier it lands, the more total interest it eliminates. Applying $20,000 in month 12 of a 30-year mortgage saves meaningfully more interest than applying the same $20,000 in month 200, even though the dollar amount is identical, simply because it has more remaining months to stop compounding against.
Frequently asked questions
How is a one-time payment different from the Extra Payment calculator?
This models a single lump sum applied once (like a bonus or tax refund), while the Extra Payment calculator models a recurring amount added to every monthly payment — use whichever matches how you actually plan to pay.
When during the loan does a lump-sum payment save the most interest?
The earlier you apply it, the more interest it saves — because it reduces the principal balance that interest accrues on for the entire remaining term, so an early lump sum compounds its savings over more remaining payments.