Bitcoin Halving API

Base URL

https://why21million.com/api

Authentication

No key or registration required.

Rate limit

No published limit. The response for a given height never changes, so cache it permanently.

Pricing

Free.

CORS

Enabled — callable directly from browser JavaScript

Official docs

Read the docs

Every request below was executed against the live API on 2026-08-21, and the response shown is the real body it returned — not an illustration.

curl 'https://why21million.com/api/halving/850000'

const res = await fetch("https://why21million.com/api/halving/850000");
if (!res.ok) throw new Error(`Request failed: ${res.status}`);
const data = await res.json();
console.log(data);

import requests

res = requests.get("https://why21million.com/api/halving/850000", timeout=20)
res.raise_for_status()
print(res.json())

{
  "height": 850000,
  "era": 5,
  "rewardBtc": 3.125,
  "blocksIntoEra": 10000,
  "blocksUntilNextHalving": 200000,
  "nextHalvingBlock": 1050000,
  "source": "https://why21million.com/book/halving-schedule/"
}

heightinteger

The height you asked about, echoed back.

erainteger

Which halving era the height falls in, counting from 1 for the original 50 BTC subsidy.

rewardBtcnumber

Block subsidy in BTC at that height. Excludes transaction fees, which are separate.

blocksIntoErainteger

How far into the current era the height sits.

blocksUntilNextHalvinginteger

Blocks remaining to the next halving — a count, not a duration.

nextHalvingBlockinteger

The exact height at which the next halving occurs.

sourcestring

Link to the schedule reference the arithmetic follows.

• Build a halving countdown widget from a current block height
• Show the block subsidy applicable at a historical height
• Verify your own halving arithmetic against a reference implementation
• Explain issuance in educational content about Bitcoin