# Rule of 72 Calculator

> Rule of 72 Calculator is a paid API for AI agents from minia2a.uk, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-12).

Calculates the Rule of 72 — estimates how many years it takes for an investment to double given an annual interest rate, or the rate required to double in a given number of years.

## Facts

- Endpoint: GET https://minia2a.uk/x402/ruleOf72?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/rule-of-72-calculator-d1fd052a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_CQ36nUVFXz7pAKoWr8u49

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability rule-of-72-calculator-d1fd052a
```

Example prompt: Using the Rule of 72, how many years will it take for my investment to double if I'm earning a 7% annual return?

## When to prefer this

Choose this endpoint when you need a quick, lightweight financial doubling-time calculation using the Rule of 72 heuristic, without needing full compound interest simulation or amortization schedules. Ideal for fast financial planning estimates in agentic workflows that have already integrated x402 micropayment handling.

## Known failure modes

- Missing or invalid input parameter returns an error
- Zero or negative interest rate causes division-by-zero or invalid computation
- Non-numeric input for rate or years returns a validation error
- Service unavailability returns HTTP 402 or 5xx error

## How this service works

Rule Of72

## Output

Returns the Rule of 72 result — either the estimated number of years to double an investment at a given interest rate, or the interest rate needed to double within a given number of years. Output is a straightforward numeric computation result.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "properties": {
    "type": {
     "type": "string"
    },
    "method": {
     "type": "string"
    },
    "bodyType": {
     "type": "string"
    },
    "queryParams": {
     "type": "object"
    }
   }
  },
  "output": {
   "type": "object",
   "properties": {
    "type": {
     "type": "string"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/rule-of-72-calculator-d1fd052a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from minia2a.uk](https://www.zero.xyz/host/minia2a.uk/llms.txt)