How these are written
Every guide here is written by us, from the same work that goes into our applications — RiskDesk for trade risk, OptionsDesk for options, HedgeDesk for equity research and hedging, and CashDesk for tax and cash flow on irregular income. When a guide describes a formula, it is the formula the corresponding free calculator actually runs.
Three things we try to do consistently. Show the arithmetic. Every guide carries at least one worked example with real numbers, because a formula in the abstract is easy to nod along to and hard to apply. Name the assumption. Most of these methods rest on one or two assumptions that are fine until they are not, and we say which. State what it will not do. None of this is financial, investment, tax or legal advice, and none of it predicts a price.
Where to start
If you trade, start with position sizing and then risk of ruin — in that order, because the second one explains why the first one matters more than your entry signal. If you are self-employed, start with reserving tax on irregular income, which is the problem that causes more damage than any pricing mistake.