No you cannot rely on the calculators, they do not take into account other factors that affect mining. For example according to
https://www.cryptocompare.com/mining/calculator/eth?HashingPower=300&HashingUnit=MH%2Fs&PowerConsumption=140&CostPerkWh=0, my two ethereum rigs with a total hashrate of 310mh/s should be making 1,100 USD/month, but in reality they are currently making around 950 USD /month.
The calculators can only give you a rough estimate that will be close to the real results of around one week, the one month estimate obtained from the mining calculators are quite erroneous. Altcoin mining earnings have been decreasing rapidly over the past few weeks due to the rise in difficulty and drop in the prices of most altcoins.
