Cryptocurrency mining is painstaking, expensive, and only sporadically rewarding. Nonetheless, mining has a magnetic draw for many investors interested in cryptocurrency. This may be because entrepreneurial types see mining as pennies from heaven, like California gold prospectors in 1848. And if you are technologically inclined, why not do it?
Well, before you invest the time and equipment, read this explainer to see whether mining is really for you. We will focus primarily on Bitcoin.
By mining, you can earn cryptocurrency without having to put down money for it. That said, you certainly don't have to be a miner to own crypto. You can also buy crypto using fiat currency (USD, EUR, JPY, etc); you can trade it on an exchange like Bitstamp using other crypto (example: Using Ethereum or NEO to buy Bitcoin); you even can earn it by playing video games or by publishing blogposts on platforms that pay its users in crypto. An example of the latter is Steemit, which is kind of like Medium except that users can reward bloggers by paying them in a proprietary cryptocurrency called Steem. Steem can then be traded elsewhere for Bitcoin.
In addition to lining the pockets of miners, mining serves a second and vital purpose: It is the only way to release new cryptocurrency into circulation. In other words, miners are basically "minting" currency. For example, as of the time of writing this piece, there were about 17 million Bitcoin in circulation. Aside from the coins minted via the genesis block (the very first block created by Bitcoin founder Satoshi Nakamoto himself), every single one of those Bitcoin came into being because of miners. In the absence of miners, Bitcoin would still exist and be usable, but there would never be any additional Bitcoin. There will come a time when Bitcoin mining ends; per the Bitcoin Protocol, the number of Bitcoin will be capped at 21 million.
Bitcoin are mined in units called "blocks." As of the time of writing, the reward for completing a block is 12.5 Bitcoin. At today's price of about $10,000 per Bitcoin, this means you'd earn (12.5 x 10,000)=$125,000.
When Bitcoin was first mined in 2009, mining one block would earn you 50 BTC. In 2012, this was halved to 25 BTC. in 2016, this was halved to the current level of 12.5 BTC. In 2020 or so, the reward size will be halved again to 6.25 BTC.
If you want to keep track of precisely when these halvings will occur, you can consult the Bitcoin Clock, which updates this information in real time.
A number of sites, including Blockchain.info, will give you that information in real time. At the time of writing, we are at block #509504.
Miners are getting paid for their work as auditors. They are doing the work of verifying previous Bitcoin transactions. This convention is meant to keep Bitcoin users honest, and was conceived by Bitcoin's founder, Satoshi Nakamoto. By verifying transactions, miners are helping to prevent the "double-spending problem."
Double spending means, as the name suggests, that a Bitcoin user is illicitly spending the same money twice. With physical currency, this isn't an issue: Once you hand someone a greenback $20 bill to buy a bottle of vodka, you no longer have it, so there's no danger you could use that same $20 to buy lotto tickets next door. With digital currency, however, as the Investopedia dictionary explains, "there is a risk that the holder could make a copy of the digital token and send it to a merchant or another party while retaining the original."
Let's say you had one legit $20 and one really good photocopy of that same $20. If someone were to try to spend both the real bill and the fake one, someone who took the trouble of looking at both of the bills' serial numbers would see that they were the same number, and thus one of them had to be false. What a Bitcoin miner does is analogous to that--they check transactions to make sure that users have not illegitimately tried to spend the same Bitcoin twice. This isn't a perfect analogy--we'll explain in more detail below.
Once a miner has verified 1 MB (megabyte) worth of Bitcoin transactions, they are eligible to win the 12.5 BTC. The 1 MB limit was set by Satoshi Nakamoto, and is a matter of controversy, as some miners believe the block size should be increased to accommodate more data.
Note that I said that verifying 1 MB worth of transactions makes a miner eligible to earn Bitcoin--not everyone who verifies transactions will get paid out.
1MB of transactions can theoretically be as small as 1 transaction (though this is not at all common) or several thousand. It depends on how much data the transactions take up.