This guide is based upon the use of a modern incubator using micro-computer technology, and one that can accurately achieve the settings you have entered. Using properly stored eggs from healthy stock you should be able to achieve a hatch rate average in excess of 80%.

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The humidity settings below are guide for average UK conditions to achieve a weight loss of 15 – 17% during the hatching period. Test-weigh a tray of the eggs for at least the first 10 days to check weight loss. The humidity in the middle period could range from 50-65%RH, depending upon the breed, for example, thick shelled eggs from say Marans will need a very much lower humidity than other breeds.

Days 1 – 3

Set the incubator temperature to 38.00 C, and the humidity setting to 60/65%RH. Allow several hours before loading with room temperature eggs. Set the trays in the incubator to turning mode – a turning period of 

20 minutes every 2 hours is generally the best (you can leave this until day 4). Check the water supply is connected.

Days 4 – 7

Reduce the humidity setting to 55/60%RH. Leave the temperature at 38.00 C. Check the water level is OK.

Days 8 - 11

Reduce the temperature setting to 37.70 C.  Reduce the humidity setting to 53/55%RH. If your incubator has a cooling facility, set it to operate for 45 minutes cooling per day. If it does not have a cooling facility, then once per day, turn the power to the machine off and open the incubator door slightly for a period of 20 minutes, then close door and turn power back on. Again, check the water level. 

Days 12 – 17

Reduce the temperature setting to 37.60 C. Leave the humidity setting at 53/55%RH. Again, check the water level. Continue cooling operation once per day. Open air vents slightly to increase oxygen and decrease carbon dioxide whilst maintaining humidity and temperature settings.

Days 18 – 19

Cease cooling operation.

Level the turning trays and switch off the turning mechanism. Remove all eggs from the egg trays and transfer them to the hatching baskets. Reduce the temperature setting to 37.50 C. Increase the humidity setting to 65%RH. Open air vents a little more to further increase oxygen and decrease carbon dioxide and maintain humidity and temperature settings.

Days 20 – 21

Increase the humidity setting to 70% RH or higher & temperature 37.50 C. Air vents open but maintain humidity and temperature settings.

Do not open the door during the final 2 days, wait until all chicks have hatched, even if it takes longer than the 21 days.

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If you are using a cycle system with different age batches of eggs at the same time, a constant temperature of 37.60 C and humidity 53/55% RH is fine for chicken eggs. 

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© David Campbell