# ESPP Calculator API

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

Estimate ESPP shares, lookback discount, sale proceeds, taxes, and after-tax return.

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

- Slug: `espp-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/espp-calculator/

## Endpoint

`POST https://api.miniwebtool.com/v1/tools/espp-calculator/run`

## Request body

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `annual_salary` | `float` | no |  |
| `contribution_rate_pct` | `float` | no |  |
| `offering_months` | `int` | no |  |
| `discount_rate_pct` | `float` | no |  |
| `start_price` | `float` | no |  |
| `purchase_market_price` | `float` | no |  |
| `sale_price` | `float` | no |  |
| `lookback` | `str` | no | yes | no Choices: yes, no |
| `broker_fee` | `float` | no |  |
| `ordinary_tax_rate_pct` | `float` | no |  |
| `capital_gains_tax_rate_pct` | `float` | no |  |

## Example request

```json
{
  "annual_salary": 120000,
  "contribution_rate_pct": 10,
  "offering_months": 6,
  "discount_rate_pct": 15,
  "start_price": 90,
  "purchase_market_price": 100,
  "sale_price": 110,
  "lookback": "yes"
}
```

## cURL

```bash
curl -X POST https://api.miniwebtool.com/v1/tools/espp-calculator/run \
  -H 'Authorization: Bearer mwt_live_YOUR_KEY' \
  -H 'Content-Type: application/json' \
  -d '{"annual_salary":120000,"contribution_rate_pct":10,"offering_months":6,"discount_rate_pct":15,"start_price":90,"purchase_market_price":100,"sale_price":110,"lookback":"yes"}'
```

## Response envelope

```json
{
  "request_id": "01K...",
  "tool": "espp-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 ESPP Calculator API do?

Estimate ESPP shares, lookback discount, sale proceeds, taxes, and after-tax return. 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.