Mortgage Calculator With Extra Payments & Lump Sum
Stack a recurring extra monthly payment, a one-time lump sum, and an annual bonus payment on top of your normal mortgage — then see your exact new payoff date and how much interest disappears. Real amortization math, not a rough estimate.
Reviewed for accuracy: August 2026 · Amortization methodology consistent with guidance from ConsumerFinance.gov
Your Original Loan
Leave at 0 for a brand-new loan, or enter how far you already are into your current mortgage.
Add Your Extra Payments
✦ Recurring Extra Monthly Payment
✦ One-Time Lump Sum Payment
Example: enter 12 for a lump sum applied at the end of your first year (a bonus, tax refund, or inheritance).
✦ Extra Annual Bonus Payment
Time Saved
Your Payoff Timeline, Side by Side
This is the picture that actually changes people’s minds about extra payments — not the dollar figure, but seeing how much of the bar just disappears.
What $50, $150, and $300 Extra a Month Really Does
Same loan amount and rate as above, extra monthly payment only, no lump sum. This is the table I always tell people to look at first, because it shows how little it actually takes.
| Extra Per Month | New Payoff Time | Time Saved | Interest Saved |
|---|
Lump Sum vs. Recurring Extra Payments
Both strategies attack the same enemy — compounding interest on your remaining balance — but they work on different timelines.
One-Time Lump Sum
- Biggest single impact the earlier it’s applied in the loan
- Great fit for a bonus, tax refund, inheritance, or sale proceeds
- Doesn’t require ongoing budget commitment
- Effect fades the later in the loan term it’s applied
Recurring Extra Monthly Payment
- Compounds every single month for the rest of the loan
- Small amounts add up dramatically over 20–30 years
- Requires consistent budget room, month after month
- Easiest to combine with a lump sum for a stronger combined effect
Why This Calculator Runs a Full Month-by-Month Simulation
Most “extra payment” calculators online use a shortcut formula that estimates your new payoff date without actually walking through the loan month by month. That shortcut gets close, but it quietly loses accuracy the moment you combine more than one type of extra payment — say, a recurring $150 a month plus a $10,000 lump sum at month 12. This tool doesn’t take that shortcut. It walks your loan forward one payment at a time, applies your regular principal and interest split, layers on whichever extra payments you’ve entered for that specific month, and recalculates the remaining balance before moving to the next month. That’s the same mechanical process your loan servicer uses internally, just transparent instead of hidden behind a portal.
Why timing matters more than most people expect
A dollar of extra principal paid in month 3 of a 30-year loan is worth meaningfully more than the same dollar paid in month 200, because it stops accruing interest for the entire remaining life of the loan instead of just the last few years. This is the exact reason a modest lump sum right after closing, even $5,000 to $10,000, tends to outperform people’s expectations, and it’s also why waiting “until I have more to put toward it” quietly costs money every month that passes.
A note on how servicers actually apply extra money
Sending in more than your minimum payment doesn’t automatically shorten your loan. If you don’t specify otherwise, some servicers apply the overage toward next month’s payment instead of your principal balance, which defeats the entire purpose. Whenever you make an extra payment, whether recurring or a lump sum, confirm with your servicer (usually through a note in your online payment portal or a memo line on a check) that the funds should be applied directly to principal.
Frequently Asked Questions
It depends on your loan balance, rate, and how early you start, but the pattern holds up consistently: even a modest extra $100 to $150 a month on a typical 30-year loan can save tens of thousands of dollars in interest and cut two to three years off the payoff date, simply because that extra principal stops compounding interest years earlier than it otherwise would.
A lump sum applied early in the loan has an outsized one-time effect because it immediately shrinks the balance interest compounds against. Recurring extra monthly payments compound that benefit every month for the rest of the loan. Many borrowers get the best of both: a lump sum whenever one becomes available, stacked on top of a smaller recurring extra payment they can sustain long-term.
Not automatically. Unless your loan is specifically structured to recast, you typically need to instruct your servicer, in writing or through your online portal, to apply any overpayment directly to principal rather than holding it toward next month’s bill.
A biweekly plan results in 26 half-payments a year, the equivalent of 13 full monthly payments instead of 12, which works out to one extra full payment annually. You can replicate the exact same effect without a third-party biweekly service by simply adding one-twelfth of your regular payment as an extra principal payment each month in the calculator above.
Paying off your mortgage faster does reduce the total interest available to deduct in later years if you itemize, since you’ll simply be paying less interest overall. For most homeowners, the guaranteed savings from reduced interest outweighs the value of the deduction, but it’s worth a conversation with a tax professional if you itemize substantial mortgage interest.
This comes down to your mortgage rate versus realistic expected investment returns, your tolerance for risk, and how much you personally value the certainty of a paid-off home. A mortgage rate above roughly 6 to 7 percent often favors extra payments since that return is locked in and guaranteed, while a lower rate can make investing the difference more attractive to some borrowers financially, even though many people simply prefer the peace of mind of debt freedom regardless of the math.
Yes. Enter your recurring extra monthly amount, a one-time lump sum with the month it will be applied, and an optional extra annual bonus payment, all at once. The calculator simulates all three layered together month by month to give you one combined payoff date and interest total.
Use the “Years Already Paid” field to tell the calculator how far into your current term you are. It will run the extra-payment simulation against your remaining balance and remaining term rather than assuming you’re starting from month one.
The dollar-for-dollar interest savings shrink the later you are in the loan, since less of each remaining payment goes toward interest anyway. Extra payments still shorten your payoff date at any point, but the biggest interest savings come from starting as early as you reasonably can.
No, your required monthly payment stays the same unless you specifically request a loan recast from your servicer. Extra payments shorten the loan and reduce total interest, but your minimum required payment amount doesn’t change unless you ask for that adjustment.
Most conventional, FHA, and VA loans issued in recent years don’t carry prepayment penalties, but some loan types and older loans do. Check your loan documents or ask your servicer directly before making large extra payments if you’re unsure.
A basic amortization calculator shows your standard schedule with no extra payments. This tool runs that same schedule but layers in recurring extra monthly payments, a one-time lump sum, and an annual bonus payment simultaneously, then shows the side-by-side difference in payoff date and total interest.
Related Mortgage Calculators
- Mortgage Calculators Hub — browse every state-specific and loan-program calculator on DexoCalc, including amortization, refinance, and closing cost tools alongside this extra-payment calculator.
- Main Mortgage Calculator — start here first if you want your full standard PITI payment (taxes, insurance, PMI, HOA) before layering in extra payments and a lump sum.