# Mortgage Payment Calculator

> Computes the monthly principal-and-interest payment of a fixed-rate mortgage from home price, down payment, rate and term, then adds property tax, home insurance and HOA dues to give the full monthly housing payment and lifetime interest.

- Calculator id: `mortgage-payment` · Category: Finance (`finance`) · Tool name: `calculate_mortgage_payment`
- Canonical page: https://tttkmbb.com/finance/mortgage-payment · This document: https://tttkmbb.com/finance/mortgage-payment.md · JSON definition: https://tttkmbb.com/finance/mortgage-payment.json

## Purpose

Computes the monthly principal-and-interest payment of a fixed-rate mortgage from home price, down payment, rate and term, then adds property tax, home insurance and HOA dues to give the full monthly housing payment and lifetime interest.

**Use when:** You want the monthly cost of buying a home with a fixed-rate mortgage, including escrowed taxes and insurance, or the total interest over the loan.

**Do not use when:** The loan is adjustable-rate or interest-only, or you only need the payment on a plain loan amount (use loan-payment).

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `home_price` | number |  | required | Purchase price of the property. (> 0, max 1000000000000) |
| `down_payment` | number |  | optional, default 0 | Cash paid up front; loan_amount = home_price − down_payment. For 20 % of a 250,000 home enter 50000. (min 0, max 1000000000000) |
| `annual_rate_percent` | number | % | required | Fixed note rate in percent; the monthly rate is this / 12. (min 0, max 100) |
| `term_years` | number | years | optional, default 30 | Loan term in years (30 and 15 are the common US terms). (> 0, max 50) |
| `annual_property_tax` | number |  | optional, default 0 | Yearly property tax; one twelfth is added to the monthly payment. (min 0, max 1000000000) |
| `annual_home_insurance` | number |  | optional, default 0 | Yearly homeowners insurance premium; one twelfth is added monthly. (min 0, max 1000000000) |
| `monthly_hoa` | number |  | optional, default 0 | Monthly homeowners-association or condo fee. (min 0, max 10000000) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `loan_amount` | number |  | home_price − down_payment. |
| `loan_to_value_percent` | number | % | loan_amount / home_price × 100; above 80 % usually requires mortgage insurance (PMI). |
| `monthly_principal_and_interest` | number |  | Level monthly amortizing payment on the loan. |
| `monthly_property_tax` | number |  | annual_property_tax / 12. |
| `monthly_insurance` | number |  | annual_home_insurance / 12. |
| `monthly_hoa_fee` | number |  | monthly_hoa as entered. |
| `total_monthly_payment` | number |  | Principal & interest + tax + insurance + HOA (PITI + HOA). |
| `number_of_payments` | integer |  | 12 × term_years. |
| `total_interest` | number |  | Interest paid over the full term. |
| `total_of_payments` | number |  | monthly_principal_and_interest × number_of_payments. |
| `payoff_summary` | string |  | Plain-language summary of the loan schedule. |

## Formula

`loan_amount = home_price − down_payment; i = annual_rate_percent / 1200; n = 12·term_years; P&I = loan_amount × i / (1 − (1 + i)^−n) (loan_amount / n if i = 0); total_monthly_payment = P&I + annual_property_tax/12 + annual_home_insurance/12 + monthly_hoa.`

Standard fixed-rate amortization with monthly compounding. Private mortgage insurance, closing costs and escrow cushions are not included; add PMI (typically 0.5–1.5 % of the loan per year) to the total when loan_to_value_percent exceeds 80 %.

## Data Sources

- CFPB – Owning a Home: loan costs and monthly payment components — https://www.consumerfinance.gov/owning-a-home/ (government, retrieved 2026-09-23)
- Wikipedia – Amortization calculator (annuity payment formula) — https://en.wikipedia.org/wiki/Amortization_calculator (reference, retrieved 2026-09-23)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/mortgage-payment?home_price=…&annual_rate_percent=…`
- `POST https://tttkmbb.com/api/v1/calculate/mortgage-payment` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/mortgage-payment · OpenAPI operationId `calculate_mortgage_payment` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool: `calculate_mortgage_payment` (dedicated) or `run_calculator` with `{"calculator_id": "mortgage-payment", "inputs": {…}}`

## Example

- 250,000 home, 50,000 down, 6 % for 30 years, 3,000 tax, 1,200 insurance: inputs `{"home_price":250000,"down_payment":50000,"annual_rate_percent":6,"term_years":30,"annual_property_tax":3000,"annual_home_insurance":1200}` → `{"loan_amount":200000,"loan_to_value_percent":80,"monthly_principal_and_interest":1199.1,"monthly_property_tax":250,"monthly_insurance":100,"total_monthly_payment":1549.1,"number_of_payments":360,"total_interest":231676.38,"total_of_payments":431676.38}`
- 400,000 home, 80,000 down, 6.5 % for 30 years: inputs `{"home_price":400000,"down_payment":80000,"annual_rate_percent":6.5,"term_years":30}` → `{"loan_amount":320000,"monthly_principal_and_interest":2022.62,"total_monthly_payment":2022.62,"total_interest":408142.36}`

```
GET https://tttkmbb.com/api/v1/calculate/mortgage-payment?home_price=250000&down_payment=50000&annual_rate_percent=6&term_years=30&annual_property_tax=3000&annual_home_insurance=1200
```

## Limitations

The loan is adjustable-rate or interest-only, or you only need the payment on a plain loan amount (use loan-payment). Standard fixed-rate amortization with monthly compounding. Private mortgage insurance, closing costs and escrow cushions are not included; add PMI (typically 0.5–1.5 % of the loan per year) to the total when loan_to_value_percent exceeds 80 %. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**What does PITI mean?**

Principal, Interest, Taxes and Insurance: the four components lenders count as the housing payment. total_monthly_payment is PITI plus any HOA dues.

**Why is my lender's quote slightly different?**

Lenders round the payment to cents, may include PMI or an escrow cushion, and property tax and insurance change every year while this calculator holds them constant.

**How does a 15-year term compare?**

Set term_years=15: the monthly payment rises but total interest falls sharply (200,000 at 6 % costs 231,676 interest over 30 years but 103,788 over 15 years).

## Related

- [Loan Payment Calculator](https://tttkmbb.com/finance/loan-payment.md) — Bare amortization without taxes and insurance.
- [Debt Payoff Calculator](https://tttkmbb.com/finance/debt-payoff.md) — See how extra monthly payments shorten the loan.
- [Compound Interest Calculator](https://tttkmbb.com/finance/compound-interest.md) — Compare with investing the down payment instead.