Loan Payoff Calculator
Calculate months to payoff, total interest, and total amount paid for a loan given principal, annual rate, and monthly payment.
⚡ 1 credit per call
Try it
Fill in the fields below and hit Send.
Why use this
LLMs can't reliably iterate through amortisation schedules. Use this when you need accurate loan payoff timelines, total interest costs, or to check whether a monthly payment is sufficient to ever pay off a loan.
Input
| Field | Type | Required | Description |
|---|---|---|---|
principal |
number | ✓ | Loan principal amount |
annual_rate_pct |
number | ✓ | Annual interest rate as a percentage (e.g. 4 for 4%) |
monthly_payment |
number | ✓ | Fixed monthly payment amount |
Response
| Field | Values | Description |
|---|---|---|
principal |
number | Original loan amount |
months_to_payoff |
number | Number of months until paid off |
total_interest |
number | Total interest paid over the loan term |
total_paid |
number | Total amount paid (principal + interest) |
error |
payment_too_low |
Returned when payment doesn't cover monthly interest |
minimum_payment |
number | Minimum payment needed to cover interest (only when error is set) |
API Reference
Endpoint
POST https://api.lightningapi.tools/loan-payoffRequired headers
Authorization: Bearer <apiKey>
Content-Type: application/json
Example request
{
"principal": 200000,
"annual_rate_pct": 4,
"monthly_payment": 955
}
Example response
{
"principal": 200000,
"months_to_payoff": 299,
"total_interest": 85545.00,
"total_paid": 285545.00
}