Turns out the consensus countdown to bitcoin’s fourth halving isn’t quite as predictable as the New Year’s Eve variety. 

What’s known: the fourth halving is scheduled to occur at block 840,000, which mining firms including Luxor Technologies and NiceHash have determined to happen between April 19 and April 21. 

With a current block height of 838,924, Bitcoin needs 1,076 more blocks until its codebase executes changes to halve the network’s mining subsidy reward from 6.25 BTC to 3.125 bitcoins (BTC). Though the math seems predictable Bitcoin-focused firms have not reached a consensus on the precise timing of the halving 

That poses a problem for investors, traders, and miners trying to pin down exactly what day the halving will take place to adjust operational or trading strategies accordingly.

Read more: Bitcoin’s Fourth Halving Is Right Around the Corner. Is It Still a Good Time to Buy?

Joe Downie, NiceHash’s chief marketing officer, said it’s possible to estimate when the halving will hit by subtracting current block height from the halving’s projected block height and multiplying the result by 10 minutes — the average interval between blocks.

But the method doesn’t account for block time variability, which “can significantly deviate” from the norm, Downie told Unchained in an email. 

Others may be confident on the date, but shaky on the time. Colin Harper, Luxor’s head of content and research Colin Harper, said his team is “pretty confident in April 19.” NiceHash, however, estimates the halving will occur on April 21 at 6:40 UTC, while data application website Timechain Calendar predicts April 20 at 5:34 a.m. EST.

Read more: Bitcoin Miners Diversify Their Revenue Streams as Halving Nears 

The calculation variability stems from projections with discrepancies on average block times, with firms using different timeframes to draw their averages, according to Harper.

If average block times are less than 10 minutes, the halving event will “appear to be sooner,” but if the average block time is more than 10 minutes, Bitcoin’s fourth halving “will seem to be delayed,” Downie added. 

Bitcoin’s average block time from the last halving, on May 11, 2020, clocked in at 9 minutes and 40 seconds, according to Harper. That supports the fourth halving taking place on April 19.  

“A LOT of hashrate would need to come online (and thus speed up block production) to move the date up to the 18th, and conversely, A LOT would have to come offline (and thus slow block production) for the Halving to be pushed back to the 20th,” Harper said.