# How are there over 18M bitcoins when the reward halves every 210,000 bitcoins?

A quick google search told me that up to today, more than 18.78 million bitcoins have been mined. Source

Another google search told me that today, the mining reward is 6.25 bitcoin per block.

If the above data is correct, I wonder why my calculation doesn't add up:

• According to the rules by Nakamoto, the reward becomes half after every 210,000 bitcoins are mined.
• The initial reward is 50 BTC/block, but now the reward is 6.25 BTC/block, this means the reward has been cut in half 3 times, meaning around 630,000 to 840,000 bitcoins have been mined.

Then how come the first link tells me it's 18.78 million? I must have done something wrong. Please point it out. Thank you!

Edits:

I know where I'm wrong now. "210,000 bitcoins are mined" aren't correct; it's supposed to be 210,000 blocks

• The first 210000 blocks permitted mining up to 50 BTC each. That's 50 * 210000 = 10500000 BTC, or 10.5M BTC in total at block 210000.
• The second 210000 blocks permitted mining up to 25 BTC each. That's 25 * 210000 = 5250000 BTC, or 15.75M BTC in total at block 420000.
• The third 210000 blocks permitted mining up to 12.5 BTC each. That's 12.5 * 210000 = 2625000 BTC, or 18.375M BTC in total at block 630000.
• The fourth 210000 blocks permit mining up to 6.25 BTC each, but as of writing, only 75572 such blocks have been mined. That's 6.25 * 75572 = 472325 BTC, or 18.847M BTC in total at block 705572.

The actual number is slightly lower due to various reasons where coins have been failed to be claimed, or burned. See https://bitcoin.stackexchange.com/a/38998/208 for details on various ways this has happened.

A new block is mined on average every 10 minutes. Therefore to calculate the total Bitcoin mined in a year is approximately:

Block reward x 6 x 24 x 365.25

In the first year (post the genesis block in 2009) the block reward was 50 and so:

50 x 6 x 24 x 365.25 = 2.630 million (3 decimal places)

meaning around 630,000 to 840,000 bitcoins have been mined

I'm not sure how you calculated this but you made an error somewhere.

• Every time a reward cut in half, 210K BTC has already been mined. So from 50 BTC/block to 6.25 BTC/block, the reward has been cut in half 3 times, hence 3 * 210K = 630K
– Erin
Commented Oct 18, 2021 at 15:48
• In my calculation 2.63 million were mined in a single year. The reward is cut in half approximately every 4 years. So no, 210K BTC were not mined between the genesis block and the block reward changing to 25 BTC. Commented Oct 18, 2021 at 15:53
• I see. So I must have had the information wrong? The rate the reward cuts into half is based on time (years), not based on the total amount of BTCs having been mined?
– Erin
Commented Oct 18, 2021 at 15:55
• It is based on time (blocks). The maximum that can be mined is ~21 million but it is possible for miners to claim less than the current block reward (but not more). So the total mined ever will most likely be slightly below 21 million. Commented Oct 18, 2021 at 15:59