Where the 4 Year Cycle Comes From
4628 sats \ 14 comments \ @jimmysong 1 Feb bitcoin
Every 4 years, there's a halving, and there has been endless speculation about this design decision by Satoshi. Is it to coincide with presidential election years in the US? Or the Olympics? Why 4 years? I'm not going to speculate on geo-political reasons here, but I will show you why there's a 4-year cycle and how it's related to the 21 million Bitcoin limit.
If you've watched rent, there's a famous song from it called 525,600 Minutes. That's how many minutes are in a 365-day year. And if you multiply that by 4, you get 2,102,400 minutes. Of course, there's a leap day to consider and that gives us another 60 * 24 = 1440 minutes for a grand total of 2,103840 minutes.
What's remarkable about this number is how close it is to 2.1M. And indeed, if every block is 10 minutes, 2.1M minutes turns out to be 210,000 blocks. And that's the real number for the halving cycle, not a specific 4 years. And indeed, 4 years is slightly longer, by 3840 minutes or 64 hours or 2 2/3 days. The 4 year cycle is really a ~3.96 year cycle, strictly speaking because of this extra overhang.
Block 840,000 will start the 5th epoch of Bitcoin (looking to be around April 20, 2024), which will have 3.125 BTC as a block reward. And that block reward halving every 210,000 blocks is how we get a 21M limit.
The first epoch's block reward was 50, the next 25, the next 12.5 and so on. If you add these block rewards up, that's 100 * 210,000 or 21M. But since we represent these with 0's and 1's and don't have infinite precision, the actual complete amount is slightly less at 20,999,999.9769 BTC.
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751 sats \ 1 reply \ @Enemy_of_the_state 1 Feb freebie
4/20 halving will be dope
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20 sats \ 0 replies \ @f6287b82CC84bcbd 2 Feb
Yeah 4/20 day halving in Thailand is where its at. All about the HASH rate
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729 sats \ 0 replies \ @arrivederci 2 Feb
but I will show you why there's a 4-year cycle and how it's related to the 21 million Bitcoin limit
With respect (and I mean it) this post doesn't actually show why there's a 4 year cycle (the first part), i.e. why Satoshi chose 4 years and not say 2 or 5. What it does show is how the 4 year cycle with 10 minute block times is related to the 21 million limit (the second part).
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210 sats \ 0 replies \ @0xbitcoiner 1 Feb
That's interesting. It's due to the fact that we only have 8 decimal places of accuracy.
/** Amount in satoshis (Can be negative) */
typedef int64_t CAmount;

/** The amount of satoshis in one BTC. */
static constexpr CAmount COIN = 100000000;

CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
{
    int halvings = nHeight / consensusParams.nSubsidyHalvingInterval;
    // Force block reward to zero when right shift is undefined.
    if (halvings >= 64)
        return 0;

    CAmount nSubsidy = 50 * COIN;
    // Subsidy is cut in half every 210,000 blocks which will occur approximately every 4 years.
    nSubsidy >>= halvings;
    return nSubsidy;
}
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31 sats \ 0 replies \ @DEADBEEF 1 Feb
That is very clever and I never put that together before. Satoshi Nakamoto really was a genius.
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10 sats \ 0 replies \ @f6287b82CC84bcbd 2 Feb
Maths is the language of the universe. Everything speaks in numbers
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10 sats \ 0 replies \ @kingzing131 2 Feb
Satoshi planned it all out, halving news for the pump and media cannot ignore it
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10 sats \ 1 reply \ @JustinGoldberg 2 Feb
I just realized that the halving occurs in leap years.
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10 sats \ 0 replies \ @JustinGoldberg 2 Feb
Also very interestingly, the Great pyramid of Giza is 2,103,840 blocks.
Just kidding. I made that up 😄
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11 sats \ 1 reply \ @nullama 2 Feb
the actual complete amount is slightly less at 20,999,999.9769 BTC.
The actual maximum amount is quite a bit less because of some interesting things, like for example at block 501,726 the miner did not claim the reward, so they are forever out of circulation, bringing the total down from 21M.
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0 sats \ 0 replies \ @nefinn 3 Feb
Lol, interesting.
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1 sat \ 0 replies \ @nullama 2 Feb
Yeah, but that assumes we will have the same precision when the last blocks are mined in 2140
Most definitely we will have more precision at that time.
If anything, there will need to be a rewrite of the software to solve the year 2106 problem (similar to the year 2038 problem but for unsigned integers)
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0 sats \ 0 replies \ @kurszusz 2 Feb
Interesting approach, I never thought of that. But seems like you're right, because "math never lies"
Thank you for sharing this with us!
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0 sats \ 0 replies \ @piecover 2 Feb
If you want you can listen to it here too https://translate.google.com/?sl=auto&tl=en&text=Every%204%20years%2C%20there%27s%20a%20halving%2C%20and%20there%20has%20been%20endless%20speculation%20about%20this%20design%20decision%20by%20Satoshi.%20Is%20it%20to%20coincide%20with%20presidential%20election%20years%20in%20the%20US%3F%20Or%20the%20Olympics%3F%20Why%204%20years%3F%20I%27m%20not%20going%20to%20speculate%20on%20geo-political%20reasons%20here%2C%20but%20I%20will%20show%20you%20why%20there%27s%20a%204-year%20cycle%20and%20how%20it%27s%20related%20to%20the%2021%20million%20Bitcoin%20limit.%0AIf%20you%27ve%20watched%20rent%2C%20there%27s%20a%20famous%20song%20from%20it%20called%20525%2C600%20Minutes.%20That%27s%20how%20many%20minutes%20are%20in%20a%20365-day%20year.%20And%20if%20you%20multiply%20that%20by%204%2C%20you%20get%202%2C102%2C400%20minutes.%20Of%20course%2C%20there%27s%20a%20leap%20day%20to%20consider%20and%20that%20gives%20us%20another%2060%20*%2024%20%3D%201440%20minutes%20for%20a%20grand%20total%20of%202%2C103840%20minutes.%0AWhat%27s%20remarkable%20about%20this%20number%20is%20how%20close%20it%20is%20to%202.1M.%20And%20indeed%2C%20if%20every%20block%20is%2010%20minutes%2C%202.1M%20minutes%20turns%20out%20to%20be%20210%2C000%20blocks.%20And%20that%27s%20the%20real%20number%20for%20the%20halving%20cycle%2C%20not%20a%20specific%204%20years.%20And%20indeed%2C%204%20years%20is%20slightly%20longer%2C%20by%203840%20minutes%20or%2064%20hours%20or%202%202%2F3%20days.%20The%204%20year%20cycle%20is%20really%20a%20~3.96%20year%20cycle%2C%20strictly%20speaking%20because%20of%20this%20extra%20overhang.%0ABlock%20840%2C000%20will%20start%20the%205th%20epoch%20of%20Bitcoin%20(looking%20to%20be%20around%20April%2020%2C%202024)%2C%20which%20will%20have%203.125%20BTC%20as%20a%20block%20reward.%20And%20that%20block%20reward%20halving%20every%20210%2C000%20blocks%20is%20how%20we%20get%20a%2021M%20limit.%0AThe%20first%20epoch%27s%20block%20reward%20was%2050%2C%20the%20next%2025%2C%20the%20next%2012.5%20and%20so%20on.%20If%20you%20add%20these%20block%20rewards%20up%2C%20that%27s%20100%20*%20210%2C000%20or%2021M.%20But%20since%20we%20represent%20these%20with%200%27s%20and%201%27s%20and%20don%27t%20have%20infinite%20precision%2C%20the%20actual%20complete%20amount%20is%20slightly%20less%20at%2020%2C999%2C999.9769%20BTC.%0A&op=translate
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