The ideal temperature to incubate chicken eggs is about 99.5°F (37.5°C) for most of the 21‑day incubation period in a typical forced‑air incubator.

Quick Scoop

  • Aim for around 99–100°F (37.2–37.8°C) as a safe working range.
  • In the last 3 days (days 18–21) , many guides suggest dropping slightly to about 98.5°F (36.9°C) because the chicks generate their own heat.
  • Try hard to avoid going over 101–102°F for long; temperatures at or above 103°F can kill embryos quickly.
  • Keep your incubator running and stable before adding eggs, so you know it holds around 99.5°F (37.5°C) consistently.

Still‑air vs forced‑air

  • Forced‑air incubators (with a fan): sweet spot is about 99.5°F (37.5°C).
  • Still‑air incubators sometimes run a bit warmer at egg level (often quoted around 100–102°F), because heat stratifies, but the core idea is the same: close to that 99.5°F “sweet spot.”

Tiny 21‑day story

Think of the egg as a very picky little apartment for a growing chick:

  • Days 1–17 : You’re the steady landlord, holding the place at about 99.5°F with very little fluctuation so all the “construction work” (organs, bones, feathers) goes smoothly.
  • Days 18–21 : The tenant (the chick) is now producing its own heat, so you nudge the thermostat down a notch to about 98.5°F, keep things moist, and let it break the lease—er, shell—on its own schedule.

Simple rule to remember

If you remember only one line:
Keep chicken eggs at about 99.5°F (37.5°C) almost the whole time, with only a slight drop near hatch—and never let them get hot.

TL;DR: Incubate chicken eggs at about 99.5°F (37.5°C) , keep it steady, and drop slightly (around 98.5°F) in the last few days before hatch.

Information gathered from public forums or data available on the internet and portrayed here.