Rule of 72 Doubling-Time Calculator

Years to double at a rate (72/70/69.3), or the rate needed to double.

Free tier eligible — 500 calls/month with a free key from /pricing; x402 pay-per-call above quota.

Parameters

Parameter	Type	Required	Description
`annual_rate_pct`	number	optional	Annual growth rate percent (gives doubling years)
`years`	number	optional	Target doubling years (gives required rate)

Call it over MCP (JSON-RPC 2.0)

curl -s https://wingmanprotocol.com/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{"jsonrpc": "2.0", "id": 1, "method": "tools/call", "params": {"name": "rule_of_72", "arguments": {"annual_rate_pct": 0.07, "years": 30}}}'

Or plain HTTP

curl -s https://wingmanprotocol.com/tools/rule_of_72 \
  -H 'Content-Type: application/json' \
  -d '{"annual_rate_pct": 0.07, "years": 30}'

Try it live

Edit the JSON and run it — this POSTs to https://wingmanprotocol.com/tools/rule_of_72 from your browser.

This tool is x402-metered — agents pay per call with USDC on Base. The 402 response below is the standard x402 payment-requirements envelope: sign the EIP-3009 authorization and retry with the X-Payment header, or get a free key at /pricing (500 calls/month, no card, no crypto).