Is there a mortgage calculator API I can call from my own product?

Yes. Every calculation this site performs is available as a JSON REST endpoint authenticated with a bearer API key, including amortization with PMI, future value, present value, rate and periods solvers.

API access is included with the Pro plan at $9/month and scales with the tier: Pro allows 60 requests per minute, Realtor 150, and Business 600. There is no per-call charge.

How is it authenticated?

A bearer token in the Authorization header. Keys are created and revoked from your account page, and each response returns X-RateLimit headers describing your remaining quota.

Is there an OpenAPI spec or SDK?

A full OpenAPI 3.1 document is published at /api/public/v1/openapi.json, so you can generate a typed client in any language. There is also an MCP server if you want AI agents to call the calculations directly.

Can I cache or store the results?

Yes, results may be cached and stored inside your product under the terms of your plan. What you may not do is resell the raw calculation service as a competing calculator API.

What are the uptime and support commitments?

Business plan customers get priority support with a one-business-day response. Contractual uptime commitments are handled through an annual licence — ask us for terms.

For developers & product teams

A mortgage calculator API you can build on

Amortization with real PMI termination, PITI, extra-principal payoff, future value, NPV and IRR — as JSON over HTTPS. Bearer-key auth, an OpenAPI 3.1 spec, no per-call fees. From $9/month.

Read the docs See plans Talk about volume

Not financial advice. Mortgage FV Calculator is a software calculator, not a personal-finance product or advisory service. It computes standard financial functions and displays the results for your convenience. Nothing here constitutes, or is intended to constitute, financial, investment, tax, legal, mortgage, credit, or insurance advice. Always consult a qualified professional before making any financial decision.

Why not just write the formula yourself?

The payment formula is one line. Everything around it is not: PMI that stops at 80% LTV rather than running for the full term, escrow and HOA in the total outflow, extra principal that reshapes the schedule, and the IRR and NPV solvers investors expect. That is the part that quietly ships wrong.

Correct by default

PMI termination, escrow, HOA, bi-weekly and extra-principal schedules, tax-deduction modelling with SALT and debt caps — all covered by an automated test suite.

Predictable pricing

Flat monthly tiers, no per-call metering. You can put the API in a hot path without a finance conversation about every request.

Typed and documented

OpenAPI 3.1 at /api/public/v1/openapi.json generates a client in any language, and an MCP server exposes the same tools to AI agents.

One request, full schedule

cURL

curl -X POST https://mortgagefvcalculator.com/api/public/v1/mortgage \
  -H "Authorization: Bearer mfv_live_your_key" \
  -H "Content-Type: application/json" \
  -d '{
    "homePrice": 450000,
    "downPayment": 45000,
    "interestRate": 6.75,
    "loanTermYears": 30,
    "propertyTaxAnnual": 5400,
    "homeInsuranceAnnual": 1500,
    "hoaMonthly": 250,
    "pmiRate": 0.55,
    "extraMonthly": 200
  }'

JavaScript

const res = await fetch("https://mortgagefvcalculator.com/api/public/v1/mortgage", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.MFV_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    homePrice: 450000,
    downPayment: 45000,
    interestRate: 6.75,
    loanTermYears: 30,
  }),
});

// Quota state travels on every response.
const remaining = res.headers.get("X-RateLimit-Remaining");
const { summary } = await res.json();

Endpoints

Method	Path	Returns
POST	/api/public/v1/mortgage	Full amortization: monthly PITI, PMI with 80% LTV termination, total interest, payoff date, and the effect of extra principal.
POST	/api/public/v1/future-value	Future value of a lump sum plus periodic contributions, with configurable compounding and annuity timing.
POST	/api/public/v1/present-value	Present value / NPV of a cash-flow stream at a given discount rate.
POST	/api/public/v1/rate	Solve for the periodic rate implied by a payment schedule.
POST	/api/public/v1/periods	Solve for the number of periods required to reach a target balance.
GET / POST	/api/public/v1/scenarios	List or create saved scenarios so your product can persist a user's deals against their key.

Request and response schemas for every endpoint are in the developer documentation.

Rate limits by plan

Plan	Price	Requests / min	Requests / day
Pro	$9/mo	60	10,000
Realtor	$29/mo	150	50,000
Business	$49/mo	600	250,000

Need more than 250,000 calls a day, a dedicated quota, or contractual uptime? That is an annual agreement — see licensing or ask below.

API questions

Is there a mortgage calculator API I can call from my own product?: Yes. Every calculation this site performs is available as a JSON REST endpoint authenticated with a bearer API key, including amortization with PMI, future value, present value, rate and periods solvers.
What does it cost?: API access is included with the Pro plan at $9/month and scales with the tier: Pro allows 60 requests per minute, Realtor 150, and Business 600. There is no per-call charge.
How is it authenticated?: A bearer token in the Authorization header. Keys are created and revoked from your account page, and each response returns X-RateLimit headers describing your remaining quota.
Is there an OpenAPI spec or SDK?: A full OpenAPI 3.1 document is published at /api/public/v1/openapi.json, so you can generate a typed client in any language. There is also an MCP server if you want AI agents to call the calculations directly.
Can I cache or store the results?: Yes, results may be cached and stored inside your product under the terms of your plan. What you may not do is resell the raw calculation service as a competing calculator API.
What are the uptime and support commitments?: Business plan customers get priority support with a one-business-day response. Contractual uptime commitments are handled through an annual licence — ask us for terms.

Would rather not build a UI at all? Drop in the white-label calculator embed instead.