how long are laid eggs Ok for hatching?

[squeaky88]

I'm a school teacher and have hatched chick eggs

Please pardon my question if it seems unintelligent
It has been many years since I ve done this

I bought eggs to hatch but had problems with the incubator and now have a functional one.
I have paid for them with my own $$
.I got the eggs three weeks ago...do you think there is any chance of them still be incubateable... can I still incubate them to hatch?

 

[Habibs Hens]

sorry but 3 weeks is too long they prob wont hatch now

7 day is where you can pretty much get all to hatch

after 10 then its approx. 10% decrease after each day

some people have hatched older eggs but that all depends on how they are kept

eggs older than 7 days must be turned twice daily minimum and kept at 12-18 centigrade and at a humidity of 75%
that ensures the aircell doesn't evaporate before incubation and shrink wrap the chick as incubation commences