There are seven of them here, and each one answers a single question and shows you how it arrived at the answer. They all run inside your own browser, so nothing you type is ever sent anywhere, and they all open with a worked example already filled in, which means you can see what a calculator does before you change a single field.
When a calculator needs figures from a broker, it uses ours. Of the hundred brokers on this site, 88 of them publish spreads and commissions that are precise enough to actually calculate with. The rest simply describe them as "variable", and if we filled that gap with a figure that merely looked plausible, we would be making data up rather than reporting it.
Work out what a trade or a position actually costs you.
Plan a trade or an investment before you place it, from the profit on a position to the size of your future portfolio.
If you are about to place a trade and do not know how big it should be, start with position size. It is the calculation this site argues nobody should skip, and it needs pip value as an input.
If you are choosing between two brokers, the FX fee calculator converts both pricing models into the same number, and the comparison tool puts everything else side by side.
If you want the argument for trading smaller, open drawdown and set the loss per trade to what you actually risk. It is more persuasive than anything written about it, including by us.