ARM payment calculator API

Computes the post-reset payment on an adjustable-rate mortgage, applying rate = min(index+margin, initial+periodicCap, initial+lifetimeCap) to the balance remaining after the fixed period, plus the payment-shock percent. Answers 'What will my ARM payment be after it adjusts?','How much could my adjustable rate payment jump?'.

Price$0.01per request

MethodPOST

Route/v1/calc/loan-arm-payment

StatusLive

MIME typeapplication/json

Rate limit120/minute

CacheNo cache

loanarmadjustable-ratemortgagepayment-shockcapscalculator

API URLhttps://x402.hexl.dev/v1/calc/loan-arm-payment

Integration docs

Example request

{
  "principal": 400000,
  "initialRatePct": 4,
  "fixedMonths": 60,
  "totalTermMonths": 360,
  "indexAtResetPct": 5,
  "marginPct": 2.5
}

Example response

{
  "initialPayment": 1909.66,
  "balanceAtReset": 361790.05,
  "fullyIndexedRatePct": 7.5,
  "adjustedRatePct": 6,
  "adjustedPayment": 2331.02,
  "paymentShockPct": 22.06,
  "formula": "rate = min(index+margin, initial+periodicCap, initial+lifetimeCap)",
  "breakdown": {
    "principal": 400000,
    "initialRatePct": 4,
    "indexAtResetPct": 5,
    "marginPct": 2.5,
    "periodicCapPct": 2,
    "lifetimeCapPct": 5
  }
}

Input schema

{
  "type": "object",
  "required": [
    "principal",
    "initialRatePct",
    "fixedMonths",
    "totalTermMonths",
    "indexAtResetPct",
    "marginPct"
  ],
  "properties": {
    "principal": {
      "type": "number",
      "description": "Loan principal.",
      "examples": [
        400000
      ]
    },
    "initialRatePct": {
      "type": "number",
      "description": "Initial fixed-period rate in percent.",
      "examples": [
        4
      ]
    },
    "fixedMonths": {
      "type": "number",
      "description": "Length of the initial fixed period in months.",
      "examples": [
        60
      ]
    },
    "totalTermMonths": {
      "type": "number",
      "description": "Total loan term in months.",
      "examples": [
        360
      ]
    },
    "indexAtResetPct": {
      "type": "number",
      "description": "Index value at the first reset, in percent.",
      "examples": [
        5
      ]
    },
    "marginPct": {
      "type": "number",
      "description": "Lender margin added to the index, in percent.",
      "examples": [
        2.5
      ]
    },
    "periodicCapPct": {
      "type": "number",
      "description": "Per-adjustment rate cap in percent (default 2).",
      "examples": [
        2
      ]
    },
    "lifetimeCapPct": {
      "type": "number",
      "description": "Lifetime rate cap above initial, in percent (default 5).",
      "examples": [
        5
      ]
    }
  }
}

Output schema

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