"Satoshi set the total supply of bitcoins to 21 Million" is nonsense

[BlackHatCoiner]

What would make me happy is hearing how the subsidy halves every four years so there will never be more than 21 Million Bitcoins rather than Satoshi set the limit to 21 million.

Was that what you wanted? I thought you already knew about the mathematical rules that govern Bitcoin. Assuming that every 210,000 blocks a halving occurs then we have:

• 10,500,000 coins in the first 210,000 blocks.
• 5,250,000 coins in the next 210,000 blocks.
• 2,125,000 coins in the next 210,000 blocks.

This goes on and on 'til the 31st halving that each block will reward 0.00000001 coins.

— But why is it 4 years?

Because of the block interval. The network is structured in a way to always generate a block every 10 minutes on average. If you multiply 210000 with 10 minutes then you get 2.1 million minutes which is 35,000 hours or 1,458.3 days. Divide that with 365 and you'll get 3.995 years.

[hd49728]

If you're educating people about bitcoin, maybe have a cute little graph on how many bitcoins were mined in the first 4 year period before the first halving and show the math in a visual way and how it will never reach 21 Million.

21 million is a rounded number. Is it a serious problem with 21 million  BTC and 209999999.99 BTC. It is not a serious issue but I agree with you that a note for it is fine.

The 21 million figure can be used with a note and reference to 209999999.99 BTC as total supply. I remembered this issue was discussed in the past.

I could be wrong, but I get the impression that he didn't choose 21 million.  He chose 50BTC as a block reward and then chose to cut that reward in half every 210,000 blocks.  If you do the math, that just happens to work out to a bit less than 21 million (20999999.97690000 to be exact).

4 years for each halving is another rounded figure. BlackHatCoiner explained it above.
https://www.bitcoinblockhalf.com/

Past halving event dates
The first halving event occurred on the 28th of November, 2012 (UTC) at block height 210,000
The second halving event occurred on the 9th of July, 2016 (UTC) at block height 420,000
The third halving event occurred on the 11th of May, 2020 (UTC) at block height 630,000

[FatFork]

If you're educating people about bitcoin, maybe have a cute little graph on how many bitcoins were mined in the first 4 year period before the first halving and show the math in a visual way and how it will never reach 21 Million.

You're just being sarcastic now.

Maybe the lesson we learned was the pedantry we engaged in along the way.

Yep.

[buwaytress]

Pedantry can get confusing for those not willing or not able (like me) to get full-assed about it.

I honestly don't know why it's a bother to say there is a limit of 21m that will ever be produced (as a consequence of halving), agree that there are more accurate ways to say it, but we would then have to go through almost every other way we refer to Bitcoin use and rephrase them... we could get really pedantic over how we're not really sending any actual Bitcoin when we spend them, for example (but really, that's accurate enough to say, isn't it?).

[seoincorporation]

the 21 million supply is a tricky number because if you focus on the digits after the point you will realize how big the number really is. For a reason satoshi decides to add 8 zeros after the point... and that makes the number much bigger than 21 millions.

If the bitcoin price goes really high, let's say 1 btc = $10millions then the miners can adjust the transaction fees to some satoshis. And that way we will only move satoshis for a good amount of money.