Egg Fertility Calculator — Candling Schedule

At day 7, a fertile egg shows a network of thin, spider-web-like blood vessels radiating from a small dark spot (the developing embryo), often called the 'spider' appearance. A clear, uniformly yellow-orange interior with no visible structure means the egg is infertile or development stopped very early — these should be removed to avoid contaminating the incubator if they rot.

By day 14, the embryo should be noticeably larger, appearing as a dark, irregularly shaped mass that may shift slightly when the egg is moved, and the air cell at the wide end of the egg should be visibly larger than at day 7. You may also see movement if you hold still and watch for a few seconds.

Lockdown timing depends on species: chicken eggs go into lockdown around day 18 (3 days before the day-21 hatch), duck and turkey eggs around day 25 (3 days before day-28 hatch), goose eggs around day 27, and quail eggs around day 15 (3 days before day-18 hatch). At lockdown, stop turning the eggs, raise humidity significantly, and minimize opening the incubator to preserve humidity for hatching.

In the final day or two before hatching, you may hear faint peeping or scratching sounds from inside the egg, and candling (done briefly and gently at this late stage) may show the chick positioned with its head under its wing near the air cell, ready to pip through the shell into the air cell first before fully breaking through.

A blood ring — a reddish ring visible around the inside of the shell — indicates the embryo started developing but died early, usually within the first week. These eggs should be removed promptly, since they're a common source of bacterial contamination and potential explosion risk if left in the incubator with viable eggs.

Assisted hatching is controversial and should be a last resort — most chicks that pip successfully complete hatching within 24 hours without help, and intervening too early can cause fatal bleeding if the yolk sac hasn't fully absorbed. If a chick has made no progress for 24+ hours after pipping and appears to be struggling, very cautious assistance (removing tiny bits of shell at a time, checking for bleeding before proceeding) may be considered, ideally guided by experienced advice.

The core principle is the same across chicken, duck, goose, turkey, and quail — an early candling to check fertility, a mid-incubation candling to check development, and a final candling right before lockdown — but the exact days shift to match each species' total incubation length, from quail's compressed 18-day cycle to goose's longer 30-day cycle.

A dedicated egg candler produces a tightly focused, bright beam that concentrates light through the shell for a clear view of internal structures, while a diffuse phone flashlight often isn't bright or focused enough, particularly for thicker-shelled goose or duck eggs or eggs with dark shell pigmentation. A dedicated candler makes it much easier to distinguish real developmental features from shadows.