Extra Payment & Early Payoff Calculator
See exactly how adding a modest monthly amount, applying an annual tax bonus, or switching to a biweekly schedule compresses your amortization curve and eliminates thousands in interest.
$123,531.93
New accelerated debt-free horizon: 22 yr 9 mo (contractual was 360 months).
$2,189.27
Contractual monthly87 Mo
Debt eliminated early22 yr 9 mo
Total repayment time$314,606.23
Total interest leftCalculation is instantly saved in this shareable URL.
🗄️ Saved Comparison Scenarios (Side-by-Side)
Outstanding Balance Curve
Annual Schedule with Accelerated Payments
Year-by-year record of principal retirement, interest paid, and cumulative extra cash applied.
| Year | Total Paid | Principal Retired | Interest Serviced | Extra Paid | Ending Balance |
|---|---|---|---|---|---|
| Year 1 | $29,271.24 | $7,076.44 | $22,194.80 | +$3,000.00 | $342,923.56 |
| Year 2 | $29,271.24 | $7,542.83 | $21,728.41 | +$3,000.00 | $335,380.73 |
| Year 3 | $29,271.24 | $8,039.97 | $21,231.27 | +$3,000.00 | $327,340.76 |
| Year 4 | $29,271.24 | $8,569.93 | $20,701.31 | +$3,000.00 | $318,770.83 |
| Year 5 | $29,271.24 | $9,134.76 | $20,136.48 | +$3,000.00 | $309,636.07 |
| Year 6 | $29,271.24 | $9,736.85 | $19,534.39 | +$3,000.00 | $299,899.22 |
| Year 7 | $29,271.24 | $10,378.64 | $18,892.60 | +$3,000.00 | $289,520.58 |
| Year 8 | $29,271.24 | $11,062.68 | $18,208.56 | +$3,000.00 | $278,457.90 |
| Year 9 | $29,271.24 | $11,791.85 | $17,479.39 | +$3,000.00 | $266,666.05 |
| Year 10 | $29,271.24 | $12,569.03 | $16,702.21 | +$3,000.00 | $254,097.02 |
| Year 11 | $29,271.24 | $13,397.49 | $15,873.75 | +$3,000.00 | $240,699.53 |
| Year 12 | $29,271.24 | $14,280.54 | $14,990.70 | +$3,000.00 | $226,418.99 |
| Year 13 | $29,271.24 | $15,221.79 | $14,049.45 | +$3,000.00 | $211,197.20 |
| Year 14 | $29,271.24 | $16,225.06 | $13,046.18 | +$3,000.00 | $194,972.14 |
| Year 15 | $29,271.24 | $17,294.48 | $11,976.76 | +$3,000.00 | $177,677.66 |
| Year 16 | $29,271.24 | $18,434.38 | $10,836.86 | +$3,000.00 | $159,243.28 |
| Year 17 | $29,271.24 | $19,649.41 | $9,621.83 | +$3,000.00 | $139,593.87 |
| Year 18 | $29,271.24 | $20,944.53 | $8,326.71 | +$3,000.00 | $118,649.34 |
| Year 19 | $29,271.24 | $22,324.99 | $6,946.25 | +$3,000.00 | $96,324.35 |
| Year 20 | $29,271.24 | $23,796.47 | $5,474.77 | +$3,000.00 | $72,527.88 |
| Year 21 | $29,271.24 | $25,364.92 | $3,906.32 | +$3,000.00 | $47,162.96 |
| Year 22 | $29,271.24 | $27,036.73 | $2,234.51 | +$3,000.00 | $20,126.23 |
| Year 23 | $20,638.95 | $20,126.23 | $512.72 | +$2,000.00 | $0.00 |
The Mathematics of Extra Principal Payments
Lenders calculate interest using your outstanding daily or monthly balance. When you pay only the contractual minimum, the bulk of your payment in the early years goes toward servicing accumulated interest. Every additional dollar tagged as "Principal Only" directly subtracts from the interest-bearing debt, permanently eliminating all future interest compounding that that dollar would have incurred over the remaining loan term.
1. Monthly Micro-Prepayments
Adding as little as $100 per month on a $350,000 30-year mortgage at 6.5% knocks nearly 4.5 years off the amortization horizon and saves upwards of $48,000 in non-deductible interest expense.
2. The Biweekly Advantage
Switching from 12 monthly payments to biweekly payments (every two weeks) results in 26 half-payments per year. Because a year has 52 weeks, you make the mathematical equivalent of 13 full monthly payments annually without feeling a budget squeeze.
3. Prepayment Penalties
Standard conforming and prime mortgages in the United States, Australia, and the UK legally prohibit prepayment penalties on residential owner-occupied properties. However, verify with your servicer that extra funds are applied directly to principal rather than advancing the next month's due date.
Calculation Methodology & Proof
Extra payments
Any amount above the contractual payment is applied to principal the same month, which reduces future interest and shortens the term.
- Compute the contractual payment.
- Each month add extra monthly, a yearly bonus in month 12, 24, …, and an optional one-time lump sum.
- Stop when the balance hits zero; the last payment is smaller.
- Months saved and interest saved are versus the no-extra schedule.
Important Caveats & Planning Assumptions
- Servicers that treat extra as 'pay ahead' will not produce these savings.
- Biweekly is modelled as a monthly equivalent, not a true 14-day calendar.
Frequently Asked Questions
Expert answers to common questions
Where should extra money go?
To principal. Confirm the servicer applies it as a principal curtailment, not as a skipped future payment (pay-ahead).
Is biweekly actually better?
Yes, because you make the equivalent of 13 monthly payments per year. The same extra amount as a dedicated extra-monthly payment produces a similar result.
One-time vs monthly extra?
A lump sum early in the term saves more interest than the same money later, because more of the balance is still outstanding.