# Interest-Only Mortgage Calculator API

> For the complete documentation index, see [llms.txt](/llms.txt).

Interest-only payment, the payment jump when the IO period ends, and the extra interest versus a standard loan.

Use this endpoint to add the tool to your app, site, workflow, or agent without rebuilding formulas, validation, examples, and docs.

- Slug: `interest-only-mortgage-calculator`
- Category: `finance`
- Version: `2026-04-22`
- Credits per successful call: 2
- Starts on: free
- Max payload: 65536 bytes
- Privacy mode: `hash_only`
- Available on: free, starter, pro, business, scale
- Browser tool: https://miniwebtool.com/interest-only-mortgage-calculator/

## Endpoint

`POST https://api.miniwebtool.com/v1/tools/interest-only-mortgage-calculator/run`

## Request body

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `loan_amount` | `float` | no | loan principal |
| `interest_rate` | `float` | no | annual interest rate % |
| `loan_term` | `str` | no | 30 | 10 | 15 | 20 | 25 | 40 Choices: 30, 10, 15, 20, 25, 40 |
| `io_period` | `str` | no | 10 | 3 | 5 | 7 | 15 Choices: 10, 3, 5, 7, 15 |

## Example request

```json
{
  "loan_amount": 400000,
  "interest_rate": 6.5,
  "loan_term": "30",
  "io_period": "10"
}
```

## cURL

```bash
curl -X POST https://api.miniwebtool.com/v1/tools/interest-only-mortgage-calculator/run \
  -H 'Authorization: Bearer mwt_live_YOUR_KEY' \
  -H 'Content-Type: application/json' \
  -d '{"loan_amount":400000,"interest_rate":6.5,"loan_term":"30","io_period":"10"}'
```

## Response envelope

```json
{
  "request_id": "01K...",
  "tool": "interest-only-mortgage-calculator",
  "tool_version": "2026-04-22",
  "credits_used": 2,
  "result": {}
}
```

## Errors

Errors are RFC 7807 `application/problem+json`. Branch on `code`, not `title`.

## MCP

Agents can discover and call this tool through `https://api.miniwebtool.com/mcp` or `https://api.miniwebtool.com/v1/mcp` using MCP `tools/list` and `tools/call`.

## Frequently asked

### What does the Interest-Only Mortgage Calculator API do?

Interest-only payment, the payment jump when the IO period ends, and the extra interest versus a standard loan. Use it to add this utility without rebuilding formulas, validation, examples, and documentation.

### How much does one call cost?

2 credits per successful call. Failed calls do not bill.

### What parameters are required?

Required fields: (none). Full schema at `https://api.miniwebtool.com/v1/openapi.json`.

### Is this deterministic?

Yes. Same input, same output. Tool version: 2026-04-22.