Calculator
White theme · Responsive gridEnter loan details, then compare totals and payoff timing. Extra payments are applied to principal and can reduce total interest.
Example data table
This sample shows how extras and small fees can change totals. Your numbers will vary by term, rate, and payment frequency.
| Scenario | Principal | APR | Compounding | Payments | Term | Base PI | Total interest | Total cost |
|---|---|---|---|---|---|---|---|---|
| Sample with extras | $25,000 | 7.25% | Monthly | Monthly | 5 years | 497.98 | 4,193.79 | 29,326.07 |
Formula used
This calculator converts your nominal APR and compounding into an effective rate per payment period, then builds an amortization schedule.
How to use this calculator
- Enter principal, APR, and your first payment date.
- Select compounding and payment frequency to match your loan.
- Set the term in years and months, then choose payment timing.
- Add optional extras, lump sums, fees, or escrow estimates.
- Press Calculate to view totals and payoff date.
- Use the download buttons to export CSV or PDF summaries.
Compounding and payment frequency interact
When APR is compounded monthly (m=12) but you pay biweekly (p=26), the calculator converts rates so each payment reflects 12/26 of the compounding cycle. A 7.25% nominal rate becomes an effective periodic rate about 0.27% per biweekly period. More frequent payments reduce average outstanding balance and can shorten payoff even when the nominal APR is unchanged.
Periodic rate conversion matters
The periodic rate is computed as r = (1 + APR/m)^(m/p) − 1. This avoids mispricing interest when p differs from m. For example, paying weekly with monthly compounding uses m/p = 12/52, producing a smaller per‑payment rate than APR/52, yet the cumulative effect across 52 periods still aligns with the nominal definition. The effective annual rate (EAR) is (1+APR/m)^m − 1.
Extra principal shifts interest share
Adding $50 extra each period directly increases principal paid. Early in a loan, interest can exceed 60% of the scheduled payment, so directing extras toward principal reduces later interest accrual. A one‑time $500 lump sum around payment 12 can remove end‑of‑term installments, depending on rate and remaining balance. The schedule shows the interest savings and revised payoff date.
Fees and escrow change cash flow
Service fees and escrow are added to outflow but do not reduce principal. Two loans with the same PI payment can have different monthly cash requirements. Track “Total outflow” to match a budget, and compare “Total cost” to include upfront charges such as closing costs and any origination fee not financed. Financing an origination fee increases principal and compounds interest on that amount.
Using the schedule to compare scenarios
Run a baseline with no extras, then rerun with prepayments to quantify tradeoffs. Compare total interest, total PI, and payoff date, and export CSV or PDF to document assumptions. If the calculator warns about negative amortization, increase the payment, shorten the term, or reduce interest‑only periods. Consistent inputs make comparisons reliable.
FAQs
What payment does the calculator show as “Base PI”?
Base PI is the scheduled principal-and-interest payment for the amortizing portion of the term, based on your rate conversion and payment timing. Fees, escrow, and optional extra principal are shown separately.
Why is the periodic rate not simply APR divided by payments per year?
When compounding frequency differs from payment frequency, APR/p misstates interest. The calculator converts APR with r = (1+APR/m)^(m/p) − 1 so each payment period reflects the loan’s compounding convention.
How do extra payments and lump sums affect results?
Extra amounts are applied to principal in the schedule, reducing the balance faster. That lowers future interest charges and usually shortens the payoff date. The table shows the exact interest saved period by period.
What does a negative amortization warning mean?
It means the payment is not covering the interest due for a period, so the balance can increase. Increase the payment, reduce interest-only periods, shorten the term, or confirm the rate and frequency settings.
Does escrow or a service fee reduce my loan balance?
No. Escrow and service fees are added to your cash outflow but do not pay down principal. Use “Total outflow” to plan monthly affordability and “Total cost” to include upfront charges.
Can I use the exports for documentation or sharing?
Yes. The CSV includes a row-by-row schedule plus key summary fields. The PDF provides a compact summary and a formatted schedule. Run a calculation first, then download using the buttons in the results area.