21 days
If for some reason the temperature has dropped below the correct temperature on a few occasions, you could find some of your eggs only hatching on day 22, 23, or even on day 24 or 25. Whereas fertilized chicken eggs usually take exactly 21 days to hatch, most duck eggs take 28 days, apart from Muscovy ducks. As a general rule of thumb, the eggs of Muscovy ducks take 35 days, but once again, it can vary slightly depending on conditions. If on the other hand you use an incubator in order to hatch fertilized chicken eggs, they can sometimes hatch a day or two early, or they can also hatch out a few days late. Things like humidity and temperature play a significant role. Chicken eggs are incubated at 99 to 99.5 degrees. Chicken eggs incubate for 21 days. Your countdown for days starts when you put your eggs in your incubator. It does not start when the hen lays her eggs. Duck eggs are incubated at 99 to 99.5 degrees. 6. Record the day and how many eggs you've incubated on a calendar. You should be able to estimate your hatch date based on average incubation times for the bird species you want to hatch. For example, chicken eggs typically take 21 days to hatch, whereas many duck varieties and peafowl may take 28 days. 7. Turn the eggs at least three times daily. Chicken eggs have an incubation period of about 21 days and can be hatched using either a specialized incubator under carefully monitored conditions, or using a broody hen. Use these tips for hatching chicken eggs using both methods. 1 Temperature: Chicken eggs should be incubated at a temperature between 99 and 102 degrees Fahrenheit (99.5 is often considered to be ideal). 2  Avoid temperatures outside the 97–103 °F (36–39 °C). 3  range. 4  If the temperature remains beyond either extreme for several days, hatchability may be severely reduced. Related tutorials: How-To #2: The First 60 Days. General Hints. First things first-eggs should hatch in 21 days, though some may hatch a day or 2 early and some a day or 2 late, after the incubation period began. Turning. Turning is essential during the first 14 days of incubation and should be continued until 3 days prior to the eggs expected hatch day. If hand turning, always turn the eggs an uneven number of times a day, so the eggs do not spent two nights in a row in the same position. So, how long does it take for fertilized chicken eggs to hatch? The answer to that is 21 days exactly, although you need to bear in mind that this can vary, depending on a number of circumstances. If on the other hand you use an incubator in order to hatch fertilized chicken eggs, they can sometimes hatch a day or two early, or they can also hatch out a few days late. Things like humidity and temperature play a significant role. Chicken eggs require 21 days at temperatures of approximately 99-100 F to hatch successfully. I try to maintain a temperature of 99.5 F to 100 F. Make sure that you will be able to care for the incubating eggs during the hatch period.  Candling fertile chicken eggs during incubation. Once fertilized chicken eggs have been under a brooding hen or in an incubator for a period of about three or four days, you can candle the eggs to see if they've started developing. If on the other hand you use an incubator in order to hatch fertilized chicken eggs, they can sometimes hatch a day or two early, or they can also hatch out a few days late. Things like humidity and temperature play a significant role. It takes 21 days on average for an egg to hatch once incubation begins. Before placing the eggs inside, turn on the heat source and measure the temperature and humidity over a 24-hour period, making adjustments as necessary to create the optimal environment. Mothering chicken eggs is not for everyone, but if you think it might be your calling, here’s how to do it. Once a hen lays a clutch of eggs, instincts take over. They constantly fuss over them, adjusting them just so throughout the day and rarely leaving the nest for more than a few minutes. Fertile chicken eggs can be stored up to 10 days (before incubating) with little loss in hatchability – as long as you keep them out of the refrigerator. The ideal storage conditions are 55 to 60 degrees Fahrenheit and 70 to 75 percent relative humidity. 
http://www.localharvest.org/blog/26992/entry/how_long_does_it_take http://nantahala-farm.com/chicken-duck-incubate-eggs-s.shtml http://www.wikihow.com/Use-an-Incubator-to-Hatch-Eggs http://www.wikihow.com/Hatch-Chicken-Eggs http://www.backyardchickens.com/a/how-to-incubate-hatch-eggs-just-21-days-from-egg-to-chicken http://www.localharvest.org/blog/26992/entry/how_long_does_it_take http://www.theselfsufficienthomeacre.com/2014/03/how-to-hatch-chicken-eggs-in-an-incubator.html http://www.localharvest.org/blog/26992/entry/how_long_does_it_take http://modernfarmer.com/2015/04/how-to-incubate-chicken-eggs/ http://www.grit.com/animals/incubating-chicken-eggs.aspx
how long chicken eggs incubate