How Many Eggs Does an ISA Brown Lay Per Year?

Use the egg production calculator to model your specific flock.

Production ranges

Scenario	Annual eggs	Avg / week	Avg / day	When this happens
Low	~250	~4.8	~0.68	Year 3+ bird, or winter with no added light
Normal	~300	~5.8	~0.82	First-year or second-year hen, natural daylight, standard layer feed
High	~350	~6.7	~0.96	Year 1, 16-hour lighting, 17–18% protein

The Normal row is the most realistic starting point for planning. It assumes a first or second-year hen with natural daylight and a standard layer pellet. Most backyard ISA Browns land between 280 and 320 eggs per year rather than hitting the 350-egg ceiling.

ISA Brown strain note: There is no heritage version of this bird. Every ISA Brown is a hybrid cross developed by the Institut de Sélection Animale in France, so the range you get depends almost entirely on age and care, not bloodline. The catch built into that breeding is a short laying window: plan around a sharp decline after the second year, not a gradual heritage-style fade.

By year, month, week, and day

Time period	Low (~250/yr)	Normal (~300/yr)	High (~350/yr)
Per year	250 eggs	300 eggs	350 eggs
Per month (average)	~21 eggs	~25 eggs	~29 eggs
Per week (average)	~4.8 eggs	~5.8 eggs	~6.7 eggs
Per day (average)	~0.68 eggs	~0.82 eggs	~0.96 eggs
Dozens per year	~20.8 doz.	~25.0 doz.	~29.2 doz.

A hen lays one egg every 24 to 26 hours at full production. She skips days, so the daily average never reaches 1.0. Weekly and monthly totals are where the rhythm becomes predictable.

The formula

Scale to any flock size:

Factor	Multiplier
Year 1 (peak)	×1.00
Year 2	×0.84
Year 3	×0.66
Year 4	×0.50
Year 5	×0.38
Spring / Summer	×1.00
Fall (Sept–Oct)	×0.90
Winter, no supplemental light	×0.75
Winter, 16-hr light schedule	×0.95

Example: 6 hens × 6 × 0.84 (Year 2) × 0.75 (winter, no light) = 23 eggs per week.

How production drops year over year

Year	Per hen / year	Per hen / week	6-bird flock / year	6-bird flock / week
Year 1 (peak)	~300	~5.8	~1,800	~35
Year 2	~252	~4.8	~1,512	~29
Year 3	~198	~3.8	~1,188	~23
Year 4	~150	~2.9	~900	~17
Year 5	~114	~2.2	~684	~13

The decline for an ISA Brown is steeper than most breeds, and it does not stop at a set age. The first two laying seasons carry nearly all the value, so keepers who want a steady egg supply usually add two fresh pullets every other year rather than replacing the whole flock at once.

Month by month (first-year hen)

Month	Natural light only	With 16-hr coop lighting	Notes
January	18–20	23–25	Shortest days
February	19–21	23–25	Days lengthening
March	22–24	24–26	Spring production starts
April	24–26	25–27	Peak season begins
May	25–27	25–27	Full peak
June	25–27	25–27	Full peak
July	24–26	24–26	Holds well in heat
August	24–26	24–26	Light molt approaching
September	22–24	24–26	Days shortening
October	18–20	23–25	Short days, brief molt
November	17–19	23–25	Post-molt recovery
December	17–19	23–25	Minimum without lighting

Start supplemental lighting in early September, before the natural drop begins. ISA Browns respond well to it and hold close to peak through winter when the coop day runs 16 hours.

What changes the number

Strain: production vs. heritage

ISA Browns have no production-versus-heritage split to navigate, which makes them simpler than most breeds on this point. The bird is a single commercial hybrid, so the real variable is age. Output stays high through the first two seasons, then falls roughly 15 to 20 percent each year after that. The practical takeaway: buy fresh pullets on a schedule rather than expecting one flock to carry you for five or six years.

Daylight and coop lighting

ISA Browns need 14 to 16 hours of light per day to lay at full rate. Below 12 hours, production drops. This breed is a stronger winter layer than most heritage birds and often keeps producing through cold weather, but without added light you can still expect a 25 to 30 percent dip in the darkest months. A timer-controlled LED bulb extending the coop day to 16 hours removes most of that seasonal loss. Start the light in early September, before the natural drop begins.

Annual molt

Once a year, usually in fall, every hen stops laying and replaces her feathers. ISA Browns are known for an unusually light molt, often only 4 to 6 weeks, and many barely pause before laying again. In a flock of six, production does not drop to zero, since hens molt at slightly different times. Feeding 18 to 20 percent protein during the molt speeds feather regrowth by one to two weeks.

Feed protein

ISA Browns need 16 to 18 percent protein in their layer feed to maintain consistent production. Drop below 14 percent and laying falls within two weeks. Because these hens lay so heavily, they draw hard on calcium reserves, so free-choice oyster shell should be available at all times to protect shell quality and the hen’s own bones.

Heat stress

ISA Browns handle heat reasonably well for a brown layer and tend to keep producing through warm spells better than dense-feathered breeds like Orpingtons. Provide shade and constant cool water in summer. Above 95°F, most hens slow or stop laying temporarily until the heat breaks.

Broodiness

ISA Browns rarely go broody. The brooding instinct has been almost entirely bred out of them, which is part of why they lay so consistently. You will occasionally get a hen who tries to sit, but it is uncommon enough that broodiness costs the average flock almost no eggs across a year. If one does go broody, lifting her off the nest for a few days usually resets her.

Reproductive health and lifespan

This is the trade-off that defines the breed. The same intensive laying that produces 300-plus eggs a year places real strain on the body, and ISA Browns are prone to reproductive issues such as prolapse and egg-related complications as they age. Most live 2 to 5 years rather than the 6 to 8 years a heritage breed might reach. Good feed, a stress-free setup, and not over-feeding all help, but the short productive life is built into the bird.

How ISA Browns compare

First-year production, normal backyard conditions:

Breed	Annual eggs	Egg color	Type	Vs ISA Brown
ISA Brown	250–350	Large brown	Hybrid	Baseline
Golden Comet	250–320	Brown	Hybrid	Similar
Rhode Island Red	200–300	Brown	Heritage	Lower
Australorp	250–300	Brown	Heritage	Lower
Buff Orpington	180–220	Brown	Heritage	Lower
Leghorn	250–320	White	Heritage	Similar

ISA Browns are the best pick for keepers who want maximum eggs per bird in the first two years and are comfortable replacing the flock on a schedule. They are calm, beginner-friendly, and lay through winter better than most. They are a poor pick if you want birds that lay steadily for five-plus years or that breed true, in which case a heritage layer like an Australorp or Rhode Island Red is the better long-term choice.

For temperament, climate tolerance, and care details, see the full ISA Brown breed profile. Or use the breed selector quiz to compare breeds based on your specific goals and setup.

Frequently asked questions

How many eggs does an ISA Brown lay per year?

250 to 350 eggs per year in a typical backyard setting. ISA Browns are a single commercial hybrid with no heritage version, so age drives the range more than anything else. For a healthy first-year hen with adequate daylight and quality layer feed, expect 280 to 320 eggs. That works out to roughly 25 eggs per month at peak, dropping to about 18 in December without supplemental coop lighting.

How many eggs does an ISA Brown lay per week?

At peak production in year one and year two, 6 to 7 eggs per week. A realistic average across all seasons is 4.8 to 5.8 eggs per week. In winter without supplemental lighting, expect 4 to 5 eggs per week.

When do ISA Browns start laying eggs?

ISA Brown hens begin laying at 16 to 20 weeks of age, earlier than most heritage breeds. The first few eggs are often smaller or irregular in shape, which is normal. Consistent full-size production settles in two to three weeks after the first egg appears.

Do ISA Browns lay eggs in winter?

Yes, and they do it better than most breeds. ISA Browns were bred to lay year-round, so they often keep producing through cold weather when heritage hens slow to a trickle. Without supplemental light, expect production to fall by roughly 25 to 30 percent as daylight drops below 12 hours. Add a timer-controlled LED bulb to extend the coop day to 16 hours and most of that winter dip disappears.

How long do ISA Browns keep laying?

ISA Browns lay productively for 2 to 3 years. Peak production is in years one and two. Output drops roughly 15 to 20 percent per year after that, and the decline is sharper than for heritage breeds because the bird was engineered for front-loaded, high-volume laying rather than a long gentle taper.

How many eggs will 6 ISA Browns lay per year?

About 1,800 eggs per year from six first-year birds in normal backyard conditions. That is roughly 35 eggs per week, or nearly 3 dozen per week. In winter without supplemental lighting, expect about 27 eggs per week from the same flock. Use the egg production calculator to model your exact setup by month and year.

Why did my ISA Brown stop laying?

The most common causes: daylight below 12 hours without coop lighting, the annual molt in fall, feed protein below 14 percent, stress from a new flock member or predator disturbance, or illness. For ISA Browns specifically, age is the standout factor. A hen past her second laying season produces far less, and reproductive issues common to the breed can stop laying entirely, so a sudden halt in an older ISA Brown is worth watching closely.

How many ISA Browns do I need for a family of four?

Four to five hens covers a typical family of four. A household of four eats roughly 2 to 3 dozen eggs per week, which is 24 to 36 eggs. At about 5.8 eggs per week from a first-year ISA Brown, four hens give you around 23 eggs a week and five give you around 29, with a buffer for winter dips and the natural slowdown after year two. Use the eggs per family calculator to match flock size to your household exactly.

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Sources: Mile Four ISA Brown breed guide (citing University of Georgia Extension and Penn State Extension), Townline Hatchery production data, Tractor Supply ISA Brown breed guide. For health concerns about your flock, consult a licensed poultry veterinarian. Last reviewed June 2026.

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