Personal Loan Payment Calculator with Extra Payments
This calculator estimates periodic payments, payoff time, and interest paid for a personal loan. It supports standard amortization, recurring extra payments applied each period, and a single one-time extra payment applied at a specified payment number.
Results are estimates intended to help with planning. They assume a fixed nominal annual interest rate, no fees, payments applied on schedule, and that extra payments are applied directly to principal. Use your loan documents for exact numbers and consult your lender for payment posting rules.
Adds a fixed extra amount to every scheduled payment and shows shortened payoff and interest savings.
Inputs
Results
Periodic payment with extra
$550.95
Estimated payments until payoff
53.5296
Total interest with extra
$4,492.08
Interest saved vs standard
$564.84
Payments saved vs standard
6.4704
| Output | Value | Unit |
|---|---|---|
| Periodic payment with extra | $550.95 | currency |
| Estimated payments until payoff | 53.5296 | payments |
| Total interest with extra | $4,492.08 | currency |
| Interest saved vs standard | $564.84 | currency |
| Payments saved vs standard | 6.4704 | payments |
Visualization
Methodology
Calculations use standard amortization formulas: periodic rate r = annual_rate divided by payment_frequency, number of periods n = term_years × payment_frequency, and the annuity formula for level payments when r is above zero. For a zero rate a simple division is used.
Number of payments to payoff with a higher periodic payment uses the logarithmic inversion of the annuity formula. Remaining balance after k payments uses the future value formula for amortizing loans.
Design and testing practices follow general engineering and security guidelines drawn from standards such as NIST for secure handling of input/output, ISO quality principles for validation, and IEEE best practices for numerical robustness. This tool documents assumptions and rounding behavior to support reproducibility.
Worked examples
Example 1: $25,000 loan, 7.5% APR, 5 years, monthly payments. Adding $50 to each monthly payment reduces total interest and shortens payoff; see interest saved and payments saved outputs.
Example 2: Same loan, one-time $2,000 payment at payment 12 reduces the remaining balance immediately and shortens the remaining amortization; the calculator estimates the new number of payments and interest saved.
Key takeaways
Use the recurring extra mode to model disciplined ongoing additional principal contributions. Use the one-time extra mode to model lump-sum contributions such as bonuses or tax refunds.
All outputs are estimates. Differences may occur because of rounding, payment posting timing, loan fees, variable rates, or lender-specific rules. See accuracy and regulatory notes below.
Expert Q&A
Are results exact?
Results are mathematical estimates based on the inputs and stated formulas. They do not replace lender payoff statements. Minor rounding differences and lender posting rules (daily interest, application order, fees) can change actual payoff amounts.
How should I enter biweekly payments?
Choose the payments-per-year option that matches your schedule (26 for biweekly). The calculator computes periodic rate and number of periods accordingly.
What if my loan has fees or changing interest rate?
This tool assumes a fixed nominal interest rate and no added fees. For adjustable rates or loans with fees, results will be approximate. Consult your loan agreement for exact terms.
Can I model applying an extra payment directly to principal?
Yes. The one-time extra calculation assumes the extra is applied immediately to principal at the chosen payment number. If your lender applies payments differently, actual results may differ.
Why might estimates differ from my lender's payoff?
Lenders may compute accrued interest up to a specific date, apply daily interest accrual, charge fees, or use different rounding. Always request an official payoff quote from your lender for closure.
Sources & citations
- NIST - Frameworks and Best Practices — https://www.nist.gov/
- ISO - Quality and Validation Principles — https://www.iso.org/
- IEEE - Numerical and Software Engineering Practices — https://www.ieee.org/
- OSHA - General Safety and Operational Guidance — https://www.osha.gov/