Bitcoin Difficulty Prediction Mistakes in 2017

In late 2017, there are lots of popular websites displaying charts of the current Bitcoin difficulty. After looking through many of these, some are displaying the wrong numbers - and even worse, some of them are giving predictions for future difficulty changes that are also very wrong.

In this guide we go through which websites have accurate numbers for difficulty and which don't.

BitcoinWisdom Predictions are Wrong

When searching for things like 'Bitcoin Difficulty', BitcoinWisdom is normally very near the top. Although past difficulty changes on this website seem to be correct; there are two big issues - incorrect difficulty values & incorrect future predictions.

The data on this website seems to be outdated. Currently under Difficulty History the latest value is from 6th December 2017. There was a difficulty change of +17.74% on the 18th December 2017. We're writing this on the 23rd, so this should really be displayed. The difficulty is 17.74% higher than what it's suggesting - causing anyone using it to over-estimate their mining profits.

Perhaps a more severe issue is with their Bitcoin difficulty prediction. The estimated next difficulty is currently stated at -16.49% from the value on the 6th December. If someone were looking at this right now, not only would the current value be wrong - but they'd expect a difficulty decrease rather than the increase that actually happened.

An example of the impact this can have is CryptoNick. He posted a video on December 19th, currently with 51k views, where he based a statement on BitcoinWisdom's prediction: that Bitcoin's difficulty will decrease, and so cloud mining would become more profitable. In short, due to this issue - arguably through no fault of their own - the data many popular YouTubers are using for things like difficulty is wrong, and so many people invest money based on this and end up getting a lower return than they expected. In this case expecting a difficulty 34.23% less than it actually is for the next 2 weeks. Charts are Delayed

There's a related, less severe, issue with the website, where on their stats page they specify the correct current difficulty. But when clicking through to see the chart for difficulty history, in certain scenarios the chart displays a different number for the current difficulty than their homepage. We posted a video on the topic on December 19th, and at the time the difference between these numbers was around 17%.

This has since been corrected. Whether this was a bug, or that it normally takes a few days for these numbers to update on their charts - if someone were just using the chart for their calculations, they would again get the wrong difficulty value.

Are there any accurate Bitcoin difficulty charts?

In the future, we plan to add charts for Bitcoin's difficulty on our own website, For now though looks to be the best alternative, which has correct values as of writing this for the current difficulty and past difficulty changes.

In terms of calculators using the correct values; our own mining calculator currently has the correct difficulty, and alternatively the CoinWarz Bitcoin mining calculator also seems to be accurate.

Why do websites get difficulty wrong?

There are various reasons for this, but the two mains ones are the mechanics for generating data and reliance on APIs.

When generating data for pages displaying Bitcoin difficulty, generally the server that website is on would calculate this data on a timer. Often this might be done every few minutes to keep data up-to-date, but more likely developers try to only run this kind of calculation when they have to - to minimise the load on the server. Since Bitcoin's difficulty generally changes every 2 weeks, it's possible some of these websites might generate new data for these charts once every 2 weeks, or perhaps once a day.

In either case, this would cause a lag between the actual difficulty value and the value shown on charts. In scenarios where lots of new people mine Bitcoin, a difficulty change could occur after 11 or 12 days rather than 14 (as it changes every 2016 blocks rather than exactly every 14 days) - so the value could be wrong for as many as 3 days. In a worst-case scenario, given bad luck/timing, this calculation might be done a few days before each difficulty change - causing the value to be behind by as many as 10-13 days.

A related reason is API reliance. Many websites displaying cryptocurrency data don't generate all that data themselves, they use free/paid APIs instead - so they can focus on a specific task that uses for example Bitcoin's difficulty, rather than having to work it out themselves. CoinWarz for example provides a lot of their data via an API.

In principle this is good, as it allows new cryptocurrency websites to be developed more quickly; but it does mean if the API you're using gives you wrong data, your site will be displaying this incorrect data.

On top of the two issues above, it's possible a website might just make a mistake when getting Bitcoin's difficulty, so it's always a good idea to report things like this to the website's owner. They might not even be aware of the issue!

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