The formula
gain needed = 1 ÷ (1 − loss) − 1
A 30% loss leaves 70% of the account. Getting back to 100% from 70% is a gain of 30 ÷ 70, about 42.9%. At 50% down it is 100%, and at 90% down it is 900%.
Why this decides how much to risk
Small drawdowns are cheap to recover from and deep ones are not, which is the case for small risk per trade. Losing 10% needs 11% back; losing 40% needs 67%. A long losing run at 1% a trade is an uncomfortable month. The same run at 5% a trade is a 40% hole that can take half a year or more to climb out of. See how often runs like that happen with the risk of ruin simulator.
How long it takes
With a steady return per period, the time to recover is the number of periods for that return to compound up to the gain needed: the log of 1 ÷ (1 − loss) divided by the log of (1 + return). Real returns are not steady, so read it as a best case.