How to calculate hen-day lay % (and why typed percentages go wrong)
· Tamalaki Business Network Ltd
Lay percentage, also called hen-day production, tells you what share of your hens laid an egg on a given day. It is one of the most useful numbers on a layer farm, because a drop often shows a problem with feed, water, light, health or stress before you see it anywhere else.
The formula
Lay % = eggs collected ÷ hens alive that day × 100
Use the number of hens alive on that day, not the number you placed. If birds died or were sold, your count goes down, and so does the number you divide by.
Turning trays into eggs
Most farmers count in trays. A standard tray holds 30 eggs. So:
Total eggs = trays × 30 + loose eggs
A worked example
A house has 118 hens. Today you collected 3 trays and 6 loose eggs.
- Eggs: 3 × 30 + 6 = 96
- Lay %: 96 ÷ 118 × 100 = 81.4%
If you have several houses or rooms, work out each one separately and then the farm total. Add all eggs together and all hens together, then divide. Do not average the percentages of each room, because rooms with different numbers of birds would be weighted wrongly.
Why typed percentages go wrong
When lay % is worked out by hand and typed into a report, small mistakes creep in: a wrong bird count, a slip on the calculator, or a figure copied from yesterday. The eggs and total can be right while the percentage is off by a few points, which is enough to hide a real drop or cause a false alarm.
The safest habit is to record only what you count (eggs and birds) and let the percentage be calculated. FarmMate's egg sheet does this for you, and flags a total that does not match the rooms.
Keep a daily record
One day's figure tells you little. The trend over days and weeks is what matters. Write it down every day at the same time, and compare it with the target for your breed and age from the breeder's guide or your vet.