If the mining difficulty and the price of Bitcoin remain the same as it is today (including the next block reward halvening, if applicable).
Input a monthly mining difficulty change rate to see the potential impact on the breakeven period if the mining difficulty increases or decreases over time.
Input a monthly coin price change rate to see the potential impact on the breakeven period if the price of the coin increases or decreases over time.
Input a monthly difficulty change rate AND a monthly coin price change rate to see the potential impact on the breakeven period when both the price AND mining difficulty are taken into consideration.
Mining is a high-risk and unpredictable endeavor. Any claims of earning potential and profitability for a given algorithm or coin should be carefully scrutinized. Be careful when taking advice or speculating on the topic of which miner is the best to buy.
The amount of coin a miner can yield will depend on many factors including your exact percentage of hashpower in comparison to the global network, the network difficulty, your electricity costs and other costs associated with cooling and running miners, and of course, your miner's overall uptime.
It is important to consider the estimated hashrate at which a miner can operate, the power it should consume within a certain tolerance in ideal conditions, the current value of a coin and the current estimated global network hashrate of a coin. Many of the data points used in calculations can fluctuate dramatically from day to day.
The general trend is that profitability gets harder to achieve over time as existing mining equipment becomes more obsolete as more efficient and more powerful miners are manufactured and become available for purchase to the general public and put online.