The math
Guinea fowl incubation is one week longer than chicken incubation. Same protocol, just stretched: 28 days from set to hatch, lockdown on day 25, first candling around day 10.
hatch_date = set_date + 28 days
lockdown_date = hatch_date - 3 days
Frequently asked
Is it 26, 27, or 28 days?
You'll see all three numbers in different references. Under ideal incubator conditions a few keets can pip on day 26. The bulk of a clutch tends to hatch closer to day 28, so plan for 28 and treat earlier hatches as a bonus.
Why are guinea keets so much harder to hatch than chicks?
Two reasons. The shells are tougher, which means more reliance on humidity to soften the membrane before pip. And guineas are less domesticated than chickens, meaning less generations of selection for predictable incubator hatching. Hatch rates of 60 to 70% are normal even with good practice.
When should I first candle?
Day 10 is reliable. Guinea egg shells are darker and thicker than chicken eggs, which makes earlier candling harder to read. By day 10 a fertile egg shows clear veining and a visible embryo against the candler.
Can I put guinea and chicken eggs in the same incubator?
Yes if you're willing to handle the staggered hatch. Set guinea eggs first; add chicken eggs 7 days later. Both clutches hit lockdown roughly together. The complication is that you can't open the incubator during chicken lockdown when the guineas still have a few days to go - which means accepting reduced humidity for the guineas or skipping the parallel set.