Does anyone have an idea, why Satoshi selected the Bitcoin fundamentals in a way, to create 21 Million Bitcoin?
    Is there something interesting or historical about the number 21?
    Or is it because 10 minutes is a round number, 4 years the Government cycle and 50 Bitcoin per block … just because?

    The simple reason for 21 million Bitcoin lies in the 4 variables:

    1. Starting blockreward: 50 Bitcoin
    2. Block frequency: 10 Minutes
    3. Blockreward reduction timing: Every 4 years
    4. Blockreward reduction amount: 1/2
    5. (technically it is not 4 years but a certain amount of blocks, but let's ignore that rounding error)

    If you change any of the 4 variables, you get a supply different from 21 million:

    1a. Starting blockreward: 25 Bitcoin -> 10.5 Million Bitcoin
    1b. Starting blockreward: 100 Bitcoin-> 42 Million Bitcoin

    2a. Block frequency: 20 Minutes -> 10.5 Million Bitcoin
    2b. Block frequency: 5 Minutes -> 42 Million Bitcoin

    3a. Blockreward reduction timing: Every 2 years -> 10.5 Million Bitcoin
    3b. Blockreward reduction timing: Every 8 years -> 42 Million Bitcoin

    4a. Blockreward reduction amount: 3/4 -> 14 Million Bitcoin
    4b. Blockreward reduction amount: 1/4 -> 42 Million Bitcoin

    Therefore, why 21 Million? Is there any significance behind it? Has Satoshi ever said anything about that number?

    I would also be interested in any ideas or guesses. Very likely noone really knows.

    Why did Satoshi select 21 Million as the Bitcoin supply?
    byu/Knight925 inBitcoin



    Posted by Knight925

    15 Comments

    1. Below is a quote from an email that Satoshі sent to Mike Hearn on 12 April 2009.

      “My choice for the number of coins and distribution schedule was an educated guess. It was a difficult choice, because once the network is going it’s locked in and we’re stuck with it. I wanted to pick something that would make prices similar to existing currencies, but without knowing the future, that’s very hard. I ended up picking something in the middle. If Bitcoin remains a small niche, it’ll be worth less per unit than existing currencies. If you imagine it being used for some fraction of world commerce, then there’s only going to be 21 million coins for the whole world, so it would be worth much more per unit. Values are 64-bit integers with 8 decimal places, so 1 coin is represented internally as 100000000. There’s plenty of granularity if typical prices become small. For example, if 0.001 is worth 1 Euro, then it might be easier to change where the decimal point is displayed, so if you had 1 Bitcoin it’s now displayed as 1000, and 0.001 is displayed as 1.”

    2. Its because 10 minutes happens 210,000 times in 4 years and a month. Multiply that by all block rewards added together.

      210,000 X 100 = 21,000,000

    3. It’s the amount of sats that matters 2.1 quadrillion. Enough for divisablility . How many sats a bitcoin is a number bias and not relevant to a store of value with a fixed supply.

    4. Chance-Chart-8182 on

      He didn’t just pick the number… he picked the distribution schedule and that’s the number it produced.

    5. It’s because it’s half “the answer to life, the universe, and everything” the other half is for you to figure out.

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