Understanding your combined prepayment results
The table below distinguishes the two prepayment mechanisms this calculator models, since they reduce interest through slightly different paths even though both ultimately shrink the principal balance faster than the required schedule alone.
| Prepayment type | When it is applied | Effect on the amortization schedule |
|---|---|---|
| Recurring extra monthly payment | Every month, alongside the required payment | Balance declines faster every month for the life of the loan |
| One-time lump sum | Applied once, immediately | Starting balance drops instantly; all future interest is charged on the lower balance |
- This calculator assumes a fixed rate for the remaining term and that all extra funds are applied directly to principal with no prepayment penalty.
- It does not account for possible loan recasting, where a lender formally re-amortizes the loan at the new lower balance to reduce the required minimum payment — this calculator's 'new total monthly payment' assumes the recurring extra is paid voluntarily on top of the unchanged required payment.
- Figures exclude property taxes, homeowners insurance, HOA dues and PMI, which are typically collected separately from principal-and-interest payments.
What is an extra mortgage payment calculator?
This calculator models two distinct forms of mortgage prepayment together: a recurring extra amount added to every monthly payment, and a one-time lump sum applied immediately to reduce the starting balance (for example, from a bonus, tax refund or inheritance). Both reduce the principal a lender charges interest on, but they act differently — the lump sum lowers the balance the amortization schedule starts from, while the recurring extra payment chips away at the balance every month going forward.
The Consumer Financial Protection Bureau notes that any payment amount above the required minimum, whether recurring or one-time, is applied to principal on most standard mortgages (absent a prepayment penalty), which is the mechanism this calculator simulates for both prepayment types combined.
Results are compared against the loan's original schedule at its current balance and remaining term, so the combined effect of the lump sum and the recurring extra payment on payoff time and interest cost is isolated from the loan's baseline trajectory.
How to use this extra mortgage payment calculator
- Enter the current outstanding loan balance.
- Enter the loan's annual interest rate.
- Enter the number of years remaining on the loan (not the original term, unless no payments have been made).
- Enter any extra recurring monthly amount you plan to add to each payment; set it to zero if you only want to model a lump sum.
- Enter a one-time lump-sum payment if applicable; set it to zero if you only want to model recurring extra payments.
- Read the new payoff time, time saved, interest saved, and the new total monthly payment (required payment plus the recurring extra amount).
The formula behind combined extra payments
The required monthly payment is first computed on the original balance over the years remaining. The lump sum is then subtracted from the starting balance before the accelerated schedule is simulated, and the recurring extra amount is added to the required payment every month of that simulation. The baseline comparison schedule uses the original balance and the required payment alone, with no lump sum and no recurring extra.
Worked example: a $250,000 balance at 6.5% with 25 years remaining has a required payment of $1,688.02 and, on its own, would take 300 months (25 years) at that payment level. Adding a $100 recurring extra payment (no lump sum) raises the total payment to $1,788.02 and, by direct simulation, shortens the payoff to roughly 21.9 years — about 3.2 years sooner — saving roughly $37,671 in interest.
Common mistakes
- Entering years since origination instead of years remaining, which produces an inaccurate baseline schedule.
- Assuming a lump-sum payment automatically lowers the required monthly payment — on most loans it shortens the term instead, unless the loan is formally recast.
- Not confirming with the servicer that a lump-sum payment was applied to principal rather than held as a payment-in-advance credit.
- Overlooking a prepayment penalty clause that could apply to a large lump-sum payment on certain loan types.
- Double-counting savings by assuming the recurring extra and lump sum effects add together linearly — because interest compounds on a shrinking balance, the combined effect is calculated by direct month-by-month simulation, not simple addition.
Pertanyaan yang sering diajukan
What is the difference between a recurring extra payment and a lump sum?
A recurring extra payment adds a fixed amount to every monthly payment for as long as the borrower continues it, chipping away at the balance every month. A one-time lump sum is applied immediately to reduce the starting principal balance in a single transaction, after which all future interest is calculated on that lower balance. Both reduce total interest, but a lump sum's benefit is realized immediately while a recurring extra payment's benefit accrues gradually.
Can I combine a lump sum and recurring extra payments?
Yes — this calculator models both applied together: the lump sum reduces the starting balance immediately, and the recurring extra amount is then added to every monthly payment across the accelerated schedule that follows. Combining both typically produces a larger interest saving than either strategy alone.
Does an extra payment lower my required monthly payment?
Not automatically. On most standard mortgages, extra payments and lump sums reduce the balance and shorten the payoff time, but the contractual required payment stays the same unless the lender formally recasts (re-amortizes) the loan at the new balance — a separate request that some servicers charge a fee to process.
Where should a lump sum like a bonus or tax refund go — principal or savings?
This calculator only quantifies the guaranteed interest saved by applying a lump sum to mortgage principal; it does not weigh that against maintaining an emergency fund, paying down higher-interest debt, or other financial priorities. A licensed financial adviser can help evaluate the right use of a lump sum for a specific situation.
Are there penalties for making extra mortgage payments?
Most conforming U.S. residential mortgages carry no prepayment penalty, but some loan types do. The Consumer Financial Protection Bureau recommends reviewing the loan note or contacting the servicer before making a large lump-sum payment, since a penalty could reduce the net benefit calculated here.
Referensi
- Consumer Financial Protection Bureau (CFPB). How can extra mortgage payments save me money? consumerfinance.gov.
- Consumer Financial Protection Bureau (CFPB). What is a prepayment penalty? consumerfinance.gov.
- Consumer Financial Protection Bureau (CFPB). What is mortgage recasting? consumerfinance.gov.
- Fannie Mae. Selling Guide — mortgage payoff and recasting provisions. fanniemae.com.
- Brueggeman WB, Fisher JD. Real Estate Finance and Investments. 15th ed. McGraw-Hill Education, 2019.