Invoice late fee calculator API

Compute a late fee as a flat fee plus simple interest accrued over days overdue: fee = flat + principal*annualRate*daysOverdue/365, returning the interest, total fee and total due. Answers 'late fee on a $5000 invoice 30 days overdue', 'interest at 18% APR on an overdue invoice', 'how much to charge for a late payment'.

Price$0.01per request

MethodPOST

Route/v1/calc/budget-invoice-late-fee

StatusLive

MIME typeapplication/json

Rate limit120/minute

CacheNo cache

budgetinvoicelate-feeinterestoverduefreelancecalculatormoney

API URLhttps://x402.hexl.dev/v1/calc/budget-invoice-late-fee

Integration docs

Example request

{
  "invoiceAmount": 5000,
  "daysOverdue": 30,
  "annualRatePercent": 18,
  "flatFee": 25
}

Example response

{
  "invoiceAmount": 5000,
  "daysOverdue": 30,
  "annualRatePercent": 18,
  "flatFee": 25,
  "interestAccrued": 73.97,
  "totalLateFee": 98.97,
  "totalDue": 5098.97,
  "dailyRate": 2.4658
}

Input schema

{
  "type": "object",
  "required": [
    "invoiceAmount",
    "daysOverdue"
  ],
  "properties": {
    "invoiceAmount": {
      "type": "number",
      "description": "Invoice principal in dollars",
      "examples": [
        5000
      ]
    },
    "daysOverdue": {
      "type": "number",
      "description": "Days past due",
      "examples": [
        30
      ]
    },
    "annualRatePercent": {
      "type": "number",
      "description": "Annual interest rate percent (default 18)",
      "examples": [
        18
      ]
    },
    "flatFee": {
      "type": "number",
      "description": "Flat late fee in dollars",
      "examples": [
        25
      ]
    }
  }
}

Output schema

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