100 Days to the Halving
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The calendar shows there are just 100 days until Qtum’s first halving on December 1, 2021. In this blog, we review the halving math and fix a previous incorrect capped supply calculation.
The Halving
Qtum halvings are based on a 4-year interval of 3,942,000 blocks. Every 4 years the block reward drops by half and will drop from 1.0 QTUM to 0.5 QTUM on December 1st, 2021.
The calculation is 3,942,000 blocks / 2,700 blocks per day = 1,460 days, or 4 years (not considering leap years).
Qtum’s first halving calculation is a little more complicated because Qtum Chain launched with 144-second blocks, then hard forked to 128-second blocks, and finally hard forked to 32-second blocks. The halving block height will be 1,427,004, and then at every 3,942,000 additional blocks going forward.
The first halving will be coming on December 1, 2021, at approximately 11 am GMT.
Mia Culpa
In previous blogs (now corrected) I failed to account for a difference in issuance for the hard fork at block 680,000. On this hard fork to version 0.19.1, the block rewards switched from mutualized (paid out over 510 blocks) Proof-of-Stake totaling 4.0 QTUM to a single payout of 1.0 QTUM. This stranded some 509 block rewards with partial payments (blocks 679,491–679,999). These stakers were made whole with a transaction payout from existing inventory, not from newly minted coins, so the total supply was reduced by 1,818 QTUM, giving a new maximum capped supply of 107,820,588.25 reached in 2045. The charts below show this correction because we strive for accuracy!
The genesis blocks 1–5,000 created the original 100,000,000 QTUM needed for Proof-of-Stake, creating 20,000 QTUM with each block. Starting at block 5,001, the block reward subsidy was 4.0 QTUM and continuing until block 844,999. After the hard fork for 32-second blocks at block 845,000, the block reward was 1.0 QTUM in a single payment, which will be halved to 0.5 QTUM at block 1,427,004, which will take place on December 1, 2021 (depending on your time zone).
Qtum Code References
The number of blocks in the halving interval is a variable named “nSubsidyHalvingIntervalV2” and is set by the code in chainparams.cpp, which for “version 2” 32-second blocks is 3,942,000 blocks.
The first having for Qtum will be at block 1,427,004 on December 1, 2021, as controlled by the code in validations.cpp.
