Simple Interest Loan Payment Calculator

Example data table

Formula used

How to use this calculator

1. Enter the loan amount, annual rate, and term length.
2. Select term unit and payment frequency that match your offer.
3. Add any down payment and fees, then choose how fees are handled.
4. Click Calculate to view payment totals and schedule.
5. Use Download CSV or Download PDF for sharing.

Input discipline

Accurate inputs drive reliable outputs. The financed amount equals loan minus down payment, plus any fees that are rolled in. For Sample A, $10,000 with $150 financed fees becomes $10,150. At 8% for 24 months (2.00 years), add-on interest is $10,150 × 0.08 × 2 = $1,624, so total repaid is $11,774 across 24 payments. Adjust decimals to match statements.

Payment frequency effects

Frequency changes the number of payments and the cash-flow pattern. The calculator converts term into years, multiplies by payments per year, then rounds to an integer schedule. With the same rate and term, weekly payments are smaller but occur more often. Sample B shows $5,000 at 10% for 12 months with 26 biweekly payments: $500 interest, $5,500 total, and about $211.54 per payment.

Fees and net proceeds

Fees influence both cost and what the borrower actually receives. If fees are financed, they increase the principal base that earns interest for the full term. If fees are paid upfront, the financed amount is lower, but the borrower’s net proceeds drop on day one. Sample C uses $300 upfront fees: financed principal remains $20,000, while cash received is reduced by $300. Run both options to quantify the trade-off.

Schedule interpretation

This model distributes interest evenly, producing a flat interest portion each period and a steadily declining balance. Principal per payment is financed principal divided by the number of payments, so the balance falls almost linearly. The final row is adjusted to eliminate rounding drift, ensuring the ending balance reaches zero while keeping totals consistent for exports and printing. Charts make patterns easier to spot.

Decision checkpoints

Use the implied annual rate as a cross-check when comparing offers that advertise add-on interest. A lower stated rate can still produce a higher effective rate if fees are financed or the term is extended. Review total repaid, payment size, and payoff date together, and rerun scenarios with stress inputs before committing. If your contract uses declining-balance interest, results will differ.

FAQs

1) What is add-on simple interest?

Add-on interest is calculated once on the financed amount for the full term, then added to principal and split evenly across payments. The interest portion is typically flat each period, unlike amortized loans.

2) How is payment frequency handled?

The term is converted to years, multiplied by payments per year (monthly, weekly, biweekly, quarterly), then rounded to a whole number of payments. The total repay amount is divided by that count.

3) Why can the implied annual rate differ from the stated rate?

With add-on pricing, you pay interest on the full financed amount for the entire term, even as the balance declines. Financed fees and longer terms can further increase the effective annualized cost.

4) Should I finance fees or pay them upfront?

Financing fees increases the principal base used for interest, raising total cost but reducing upfront cash needs. Paying fees upfront lowers financed interest but reduces net cash received. Compare both using the same term and rate.

5) Does this match declining-balance simple interest loans?

Not exactly. This calculator uses add-on simple interest with a flat interest allocation per payment. Declining-balance methods compute interest on the remaining balance each period, which usually changes the payment split and totals.

6) Can I export and share the schedule?

Yes. Use Download CSV for spreadsheet review or Download PDF for a printable summary with the full schedule. Exports reflect the table shown, including totals and the rounding-safe final payment adjustment.