How this instrument works
Boiling an egg to a specific doneness comes down to two things: how long the heat has to penetrate to the yolk, and how much yolk there is to heat through. This calculator uses standard reference times for a large egg dropped into already-boiling water: about 6 minutes for a soft, runny-yolk finish, 8 minutes for a medium or jammy yolk, and 11 minutes for a fully set hard-boiled yolk. It then applies a small, commonly used adjustment for egg size, since a smaller egg's yolk heats through faster and a larger egg's takes a little longer.
This is deliberately the simple, standard-times approach rather than a physics-based calculation involving egg mass, starting temperature, and altitude — that more precise method exists in cooking science circles but depends on a thermal-conductivity constant that varies enough between sources to be worth treating with real caution rather than presenting as settled fact. If you're looking for that altitude-and-physics-adjusted method specifically, this calculator isn't it; it's built around the reference times most home cooks actually use.
- Choose your desired doneness: soft, medium/jammy, or hard-boiled.
- Choose your egg size.
- Read off the total boiling time in minutes, timed from when the egg goes into already-boiling water — not from a cold start.
A large egg, medium/jammy doneness
A large egg (the US standard size, so no adjustment applies) targeting a medium, jammy-yolk doneness uses the base 8-minute reference time directly: 8 + 0 = 8.0 minutes from when it goes into a rolling boil.
For comparison, the same jammy doneness in a small egg would drop to 8 + (-1) = 7.0 minutes, since a smaller yolk needs slightly less time for heat to reach its center — a small but real adjustment worth making if your carton isn't labeled 'large.'
Questions
Do I start timing from cold water or already-boiling water?
This calculator's times assume the egg goes into water that's already at a rolling boil, which is the more common and more precisely repeatable method since it gives every egg the same starting condition. If your recipe instead starts eggs in cold water and brings the pot up to a boil together, the total time will run longer and less predictably, since how fast the water heats up varies by pot, stove, and how many eggs are in it.
Why does egg size change the boiling time?
A larger egg has more yolk mass for heat to penetrate to reach the center, so it takes a little longer at the same doneness target; a smaller egg's yolk is closer to the shell's surface relative to its size, so it sets slightly faster. The adjustment used here is modest — about half a minute to a full minute either direction from the large-egg baseline — reflecting that size differences between common egg grades aren't huge, but they are enough to notice at the margins of a specific doneness.
What's the difference between this and an altitude-adjusted physics egg calculator?
Some egg-boiling calculators use a detailed heat-transfer physics model that accounts for the egg's exact mass, starting temperature, and boiling point at your specific altitude, since water boils at a lower temperature at higher elevations. This calculator intentionally uses standard reference times instead, because the physics model depends on a thermal-conductivity constant that varies enough across published sources to introduce meaningful uncertainty. If you're cooking at significant altitude, expect these standard sea-level-calibrated times to run a little short and add a minute or two.
How do I stop the egg from cooking once it's done?
Transfer it immediately into a bowl of ice water or run it under cold water for a minute or two once the timer's up — the egg keeps cooking from residual heat for a short while after it leaves the boiling water, and a quick cold shock stops that carryover cooking right at your target doneness. This also makes the shell noticeably easier to peel once the egg has fully cooled.