Loan payoff time calculator API

Solves the number of months to clear a balance at a fixed payment via n = -ln(1 - P*r/M)/ln(1+r), and rejects payments below the monthly interest. Answers 'How long until this loan is paid off?','How many months at this payment?'.

Price$0.01per request

MethodPOST

Route/v1/calc/loan-payoff-time

StatusLive

MIME typeapplication/json

Rate limit120/minute

CacheNo cache

loanpayoffamortizationdebtpaymentinterestcalculator

API URLhttps://x402.hexl.dev/v1/calc/loan-payoff-time

Integration docs

Example request

{
  "balance": 10000,
  "annualRatePct": 18,
  "monthlyPayment": 250
}

Example response

{
  "payoffMonths": 61.54,
  "payoffMonthsRounded": 62,
  "payoffYears": 5.13,
  "totalPaid": 15385.76,
  "totalInterest": 5385.76,
  "formula": "n = -ln(1 - P*r/M) / ln(1+r)",
  "breakdown": {
    "balance": 10000,
    "monthlyPayment": 250,
    "monthlyInterestRate": 0.015
  }
}

Input schema

{
  "type": "object",
  "required": [
    "balance",
    "annualRatePct",
    "monthlyPayment"
  ],
  "properties": {
    "balance": {
      "type": "number",
      "description": "Outstanding balance.",
      "examples": [
        10000
      ]
    },
    "annualRatePct": {
      "type": "number",
      "description": "Annual nominal rate in percent.",
      "examples": [
        18
      ]
    },
    "monthlyPayment": {
      "type": "number",
      "description": "Fixed monthly payment.",
      "examples": [
        250
      ]
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}