Is there any rule of thumb to calculate taxes over crypto? Like "10% of your profits". I'm sure if you make more than 500k a year you might have to pay more taxes but I'm sure there is an average that covers 90% of traders.
If it's too big of a number for you, then better remake / recover those records. Luckily you have a permanent record called the blockchain.
Again, very rough. You need concrete numbers once you do actual trading, because in the U.S. you are required to make estimated tax payments. The actual numbers can, for example, vary wildly from nearly 0% to upwards of 50%.
* These are based on a typical 15% federal tax on long-term gains and 5% for state taxes; or 35% being a comfortable average for most people's effective tax rate in the U.S. for short term gains. The 50% tax rate is approached when you have largish gains, toward $1 mil or so, and live in expensive states like New York or California.
Calculating your profits (and loses) is what these sites generally do -- that is usually the hard part, especially if you have a lot of transactions. Not to mention, the way that you calculate that differs by jurisdiction. Loses are just as important since they can have a significant benefit to the taxes you owe. I use bitcoin.tax and then export the data for my accountant to fit into the rest of my tax return.