š¦Loan Payment Calculator
Calculate the fixed monthly payment for a loan from its principal, annual interest rate and term in years, plus total repaid and total interest (annuity formula).
Worked examples
300,000 at 4.5% for 30 years
GET /api/v1/calculators/loan-payment-calculator?principal=300000&annualRate=4.5&years=30
Result: 1,520.06 / month
20,000 at 6.9% for 4 years
GET /api/v1/calculators/loan-payment-calculator?principal=20000&annualRate=6.9&years=4
Result: 478 / month
500,000 at 2% for 15 years
GET /api/v1/calculators/loan-payment-calculator?principal=500000&annualRate=2&years=15
Result: 3,217.54 / month
Machine API (x402)
$0.002 / callThis tool is also a JSON API for AI agents. Requests without payment receive 402 Payment Required plus instructions; agents pay USDC on Base via the x402 protocol ā no accounts, no API keys.
GET /api/v1/calculators/loan-payment-calculator?principal=300000&annualRate=4.5&years=30 HTTP/1.1
Host: agenttools-hub.vercel.app
ā 402 (payment required, instructions in headers)
ā 200 (after X-PAYMENT header; JSON body below)
{
"tool": "calculators/loan-payment-calculator",
"input": {"principal":300000,"annualRate":4.5,"years":30},
"result": { "value": 1520.055929, "answer": "1,520.06 / month" }
}Agent docs: /llms.txt Ā· OpenAPI spec Ā· integration guide
About this tool
Compute the fixed monthly payment of an amortized loan ā mortgage, car or personal ā from the amount borrowed, the nominal annual rate and the term. Total repaid and total interest are included so you can compare offers.
M = P Ā· r Ā· (1+r)āæ Ć· ((1+r)āæ ā 1), where r = annual rate Ć· 12 and n = years Ć 12
Frequently asked questions
Does this include taxes, insurance or fees?
No. The result is the pure principal-and-interest payment (P&I). Property tax, insurance and origination fees come on top.
Why is total interest so large on long loans?
Interest accrues on the remaining balance each month; stretching the term lowers the monthly payment but multiplies the number of interest-bearing months.
What happens at a 0% rate?
The payment is simply the principal divided by the number of months ā the formula handles this special case.