Egg Cooking Time Calculator
Find the ideal boiling time for a perfect soft, medium, or hard-boiled egg based on egg size and your preferred doneness. Removes the guesswork from one of cooking's most precise tasks.
Last updated: May 2026
About this calculator
Egg cooking time depends on the mass of the egg and how set you want the yolk and white. This calculator uses a base cooking time adjusted by an egg size factor. The formula is: cookingTime = baseTime + (baseTime × 0.125 × eggSize). Here, baseTime represents the starting duration for a small egg at your chosen doneness, and eggSize is a numeric modifier (e.g., 1 for medium, 2 for large, 3 for extra-large). Each size increment adds 12.5% of the base time, accounting for the greater thermal mass that larger eggs present. The underlying physics is heat conduction through the albumen to the yolk center; larger eggs simply require more time for the heat to penetrate fully.
How to use
Imagine you want a soft-boiled large egg where the base time is 6 minutes and the eggSize modifier is 2. Plug the values into the formula: cookingTime = 6 + (6 × 0.125 × 2) = 6 + 1.5 = 7.5 minutes. So you should boil your large egg for 7 minutes 30 seconds for a runny yolk and fully set white. For an extra-large egg (eggSize = 3) with the same base time: cookingTime = 6 + (6 × 0.125 × 3) = 6 + 2.25 = 8.25 minutes, or about 8 minutes 15 seconds.
Frequently asked questions
How does egg size affect boiling time for soft or hard-boiled eggs?
Larger eggs contain more mass, which means heat from the boiling water takes longer to penetrate to the center of the yolk. A medium egg might reach a soft-boiled state in around 6 minutes, while an extra-large egg needs closer to 8 minutes for the same result. Ignoring size differences is one of the most common reasons home cooks end up with unexpectedly runny or overcooked eggs. Using a size-adjusted formula accounts for this thermal difference precisely.
Should I start eggs in cold water or boiling water for accurate cooking times?
Starting eggs in already-boiling water gives far more consistent and predictable results, and most precise cooking-time formulas — including this one — assume you lower the egg into simmering or boiling water. Cold-start methods involve a variable heating phase that differs by pot, stove, and water volume, making timing unreliable. If you prefer the cold-start method, add approximately 1–2 minutes to the calculated time and expect some variation. For perfect precision, use boiling water and a timer.
Why do altitude and water temperature affect egg boiling times?
At higher altitudes, atmospheric pressure is lower, which causes water to boil at temperatures below 100 °C (212 °F). At 2,000 meters above sea level, water boils at roughly 93 °C, meaning less heat energy is transferred to the egg per minute. As a result, eggs take noticeably longer to cook at altitude — sometimes 20–30% more time than at sea level. If you live or cook above 1,500 meters, you should add extra time beyond the calculator's output or use a pressure cooker to restore full boiling temperature.