Short answer
For a large egg lowered into gently simmering water, begin with about 6 minutes for a runny yolk, 7 minutes for jammy and 9–11 minutes for firm. These are starting points, not universal laws.
Choose the finish
At around 6 minutes the white should be set while the yolk remains flowing. Around 7 minutes gives a thick, spoonable centre. From roughly 9 minutes the yolk becomes increasingly firm. Transfer eggs promptly to cold water when they reach the finish you want.
Why timings vary
A larger or refrigerator-cold egg needs more energy to heat than a smaller or room-temperature one. Altitude lowers the boiling point of water, while pan size and the number of eggs affect how quickly the water recovers. A vigorous boil can crack shells without making timing more accurate.
Make the result repeatable
Use eggs of the same size, lower them into water at the same stage and time from that point. Keep the water at a gentle simmer and change only one variable on the next attempt. Slightly older eggs often peel more readily than very fresh ones.