Loan desk
Extra Payment Loan Calculator
Simulate how a recurring extra payment can change payoff time and interest.
Extra Payment Loan Calculator: Compare the original repayment schedule with paying an additional fixed amount every month from the first payment onwards. See the combined regular payment, months to payoff, months saved and interest reduction. The extra amount reduces the outstanding principal after monthly interest is covered, while the original required payment remains unchanged. Runs 100% locally in your browser with zero server file uploads.
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- Calculators
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Estimated payment including extra
$4,991.54
- Months to payoff
- 59 months
- Months saved vs baseline
- 1 months
- Interest with extra payment
- $42,436.01
- Interest saved vs baseline
- $1,056.21
- Baseline total interest
- $43,492.22
Each month: interest = balance × rate ÷ 12; principal = payment + extra − interest; repeat until balance is zero.Principal, interest, and balance
Showing the first 12 payments and the final displayed payment. The engine uses the full bounded schedule.
| Month | Payment | Principal | Interest | Balance |
|---|---|---|---|---|
| 1 | $4,991.54 | $3,637.37 | $1,354.17 | $246,362.63 |
| 2 | $4,991.54 | $3,657.07 | $1,334.46 | $242,705.56 |
| 3 | $4,991.54 | $3,676.88 | $1,314.66 | $239,028.67 |
| 4 | $4,991.54 | $3,696.80 | $1,294.74 | $235,331.88 |
| 5 | $4,991.54 | $3,716.82 | $1,274.71 | $231,615.05 |
| 6 | $4,991.54 | $3,736.96 | $1,254.58 | $227,878.10 |
| 7 | $4,991.54 | $3,757.20 | $1,234.34 | $224,120.90 |
| 8 | $4,991.54 | $3,777.55 | $1,213.99 | $220,343.35 |
| 9 | $4,991.54 | $3,798.01 | $1,193.53 | $216,545.34 |
| 10 | $4,991.54 | $3,818.58 | $1,172.95 | $212,726.76 |
| 11 | $4,991.54 | $3,839.27 | $1,152.27 | $208,887.49 |
| 12 | $4,991.54 | $3,860.06 | $1,131.47 | $205,027.43 |
| 59 | $2,926.86 | $2,911.09 | $15.77 | $0.00 |
- This is an educational estimate for a fixed-rate loan with monthly compounding and monthly payments.
- Taxes, insurance, mortgage insurance, HOA dues, origination charges, and other costs are not included unless an input says otherwise.
- Actual lender terms, APR, fees, rounding, payment dates, prepayment rules, and contracts can differ. This is not a credit offer or financial advice.
Formula and worked example
Each month: interest = balance × rate ÷ 12; principal = payment + extra − interest; repeat until balance is zero.
A worked example with sample values:
| Inputs | |
|---|---|
| Loan amount | $250,000.00 |
| Annual interest rate | 6.5% |
| Term | 5 years |
| Extra monthly payment | $100.00 |
| Results | |
|---|---|
| Estimated payment including extra | $4,991.54 |
| Months to payoff | 59 months |
| Months saved vs baseline | 1 months |
| Interest with extra payment | $42,436.01 |
| Interest saved vs baseline | $1,056.21 |
| Baseline total interest | $43,492.22 |
The extra-payment recurrence
Let P be original principal, i the decimal monthly rate, n original months and E extra payment. Baseline M = P × i ÷ (1 − (1 + i)^−n), or P ÷ n at zero interest. Each month interest = opening balance × i; principal paid = min(opening balance, M + E − interest). Subtract principal paid and repeat until the balance is exhausted.
For an illustrative $12,000 at 12% over 1 year, M = $1,066.185464. With E = $200, the regular combined amount is $1,266.19. Month one charges $120 interest and reduces principal by $1,146.19. The unrounded recurrence reaches payoff in 11 months, saving 1 month. Interest falls from $794.23 to $670.30, a saving of $123.92; the final payment is only $8.45.
Verify how an overpayment is applied
CFPB's discussion of extra-payment allocation (https://www.consumerfinance.gov/archive/newsroom/consumer-advisory-stop-getting-sidetracked-by-your-student-loan-servicer/) shows why payment instructions matter. This estimate assumes the extra money reduces the same loan's principal promptly. Confirm allocation, payment dates and any contractual prepayment charges before interpreting the modelled saving as a net cash benefit.
At zero interest, overpayment can still shorten repayment but interest saved remains zero. An interest-only loan does not start with the same amortising baseline, and a balloon loan has a separate maturity balance; neither structure is modelled here. The loan amortisation calculator helps inspect the balance-and-interest mechanics behind the comparison.
How to use it
- Enter the amounts, rate and duration shown in the worked example or your own scenario.
- Calculate to update the result and review the assumptions.
- Compare the formula and example before using the result for planning.
Privacy & limitations
Inputs and calculations stay in your browser. No values are uploaded.
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Frequently asked questions
Does making extra payments lower the required monthly payment here?
No. The original payment is calculated once from principal, rate and term. The extra amount is added to it each month, which usually shortens payoff rather than recalculating a smaller required payment. A lender's recast or refinance would be a different calculation.
Can I model one annual lump sum instead of monthly extra payments?
This input applies the same extra amount every month from the start. Dividing an annual lump sum by 12 changes the timing and therefore the interest saved. Use a dated payment schedule if you need a specific bonus payment, delayed start or irregular overpayments.
Why can the last accelerated payment be much smaller?
The remaining principal may be smaller than the scheduled principal reduction. The final payment is capped at that balance plus the month's interest. The headline payment is the planned recurring amount, so multiplying it by months to payoff can overstate total repayments.
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