See the real impact of prepaying principal early. Track interest saved and months eliminated easily. Use clear reports to guide your next payment move.
| Scenario | Loan | APR | Term | One-time | Recurring | Interest Saved | Months Reduced |
|---|---|---|---|---|---|---|---|
| Sample (keep payment) | 250,000 | 7.25% | 30y | 5,000 @ month 13 | 100 / month | Varies by inputs | Often meaningful |
| Sample (recast) | 250,000 | 7.25% | 30y | 5,000 @ month 13 | 100 / month | Varies by inputs | Usually ~0 |
The monthly payment is computed using the standard fixed-rate loan equation: PMT = r·PV / (1 − (1 + r)−n)
Loan interest is calculated on the outstanding balance each month. When you add extra principal, the balance drops sooner, so the interest portion shrinks in every later payment. On a 30-year schedule (360 months), even modest recurring amounts can compress the timeline and reduce lifetime interest materially.
Two common strategies exist. Keep payment holds the original payment and uses prepayments to finish earlier, which typically maximizes interest savings. Recast payment recalculates the payment after the first prepayment, targeting the original remaining term. This often delivers payment relief while still reducing total interest.
Earlier months have the highest interest share because the balance is largest. A one-time payment in month 13 affects more future months than a lump sum made near the end. The chart compares balance paths to show how earlier reductions create a lower interest curve and a faster slope toward payoff.
Interest saved is the baseline total interest minus the prepayment scenario interest. Months reduced compares the month count to payoff. In recast mode, the month count usually stays close to the original plan, but total interest still falls because the balance is lower for the remaining months.
The CSV export provides month-by-month values for payment, interest, and remaining balance. Use it to test different extra principal amounts against your monthly budget. The PDF summary is useful for saving a snapshot, sharing with a partner, or preparing questions about payment application rules and any recast eligibility requirements.
Yes, if the lender applies it to principal. A lower balance reduces future interest charges because interest is computed on the remaining balance each period.
Recast recalculates the payment to keep the remaining term close to the original plan. You usually get a lower payment rather than an earlier payoff.
Yes. Enable one-time prepayment and disable recurring extra principal. The results will reflect only the lump-sum impact on interest and payoff timing.
Yes. Enable recurring extra principal and disable one-time prepayment. Choose start and end months to match your planned budget window.
It assumes a fixed interest rate, payments applied monthly, and prepayments applied directly to principal. Fees, escrow, and lender-specific rules are not included.
Start with an amount you can sustain without missing essentials. Compare interest saved against liquidity needs, then iterate using the chart and exports to find a comfortable balance.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.