How Many Eggs Does an ISA Brown Lay Per Year?
An ISA Brown hen lays 280 to 330 eggs per year. Realistic estimates by age, a month-by-month breakdown, and a formula for any flock size.
An ISA Brown hen lays 280 to 330 eggs per year in a typical backyard setting, more than almost any other backyard breed. The biggest variable is age: she lays at a near-constant high rate through her first two years, then output drops about 10 to 15 percent each year after that. For a healthy first-year hen in a well-managed flock, the most realistic estimate is 300 to 320 eggs annually.
Want the full picture on this breed? See our ISA Brown breed profile — temperament, care needs, and climate fit.
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 or older, post-peak decline, or a winter with no supplemental light |
| Normal | ~300 | ~5.8 | ~0.82 | First or second-year hen, natural daylight, standard layer feed |
| High | ~330 | ~6.3 | ~0.90 | Peak first-year hen, 16-hr lighting, 18% protein feed |
The Normal row is the most realistic starting point for planning. It assumes a healthy first or second-year hen on standard layer feed with natural daylight. Most backyard keepers land right here, close to 300 eggs in the first year, which is nearly an egg a day.
Age matters more than strain for this breed. There is only one ISA Brown line, so you will not find a “heritage” or “show” version that lays less. What moves your number is how old the hen is. Years one and two are the high-output window, and production falls off noticeably after that.
By year, month, week, and day
| Time period | Low (~250/yr) | Normal (~300/yr) | High (~330/yr) |
|---|---|---|---|
| Per year | 250 | 300 | 330 |
| Per month (average) | ~21 | ~25 | ~28 |
| Per week (average) | ~4.8 | ~5.8 | ~6.3 |
| Per day (average) | ~0.68 | ~0.82 | ~0.90 |
| Dozens per year | ~21 | ~25 | ~28 |
A hen lays one egg roughly every 24 to 26 hours at full production and skips a day here and there, so even a peak ISA Brown averages a little under one egg per day across a full year. The daily figure never quite reaches 1.0.
The formula
Scale to any flock size:
Weekly eggs = Number of hens × 6.5 × Age Factor × Season Factor
The 6.5 baseline is the ISA Brown’s peak rate of about six to seven eggs per week. Two breed notes before you run the numbers. ISA Browns hold winter output better than the standard season factor suggests, because they barely molt, so the winter figures below are slightly conservative for this hybrid. They also slow down a little faster than heritage breeds once past year two, so treat the Year 3 and later age factors as optimistic for this breed.
| 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 to Oct) | ×0.90 |
| Winter, no supplemental light | ×0.75 |
| Winter, 16-hr light schedule | ×0.95 |
Example: 6 hens × 6.5 × 0.84 (Year 2) × 0.75 (winter, no light) = about 25 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 | ~1,510 | ~29 |
| Year 3 | ~198 | ~3.8 | ~1,190 | ~23 |
| Year 4 | ~150 | ~2.9 | ~900 | ~17 |
| Year 5 | ~114 | ~2.2 | ~685 | ~13 |
Production slides down gradually rather than stopping at a set age. For ISA Browns the year-two-to-three drop is steeper than for most heritage breeds, so many keepers bring in two or three new pullets every second year to keep the flock average near an egg a day. That staggered approach beats replacing the whole flock at once.
Month by month (first-year hen)
| Month | Natural light only | With 16-hr coop lighting | Notes |
|---|---|---|---|
| January | 22 | 26 | Shortest days, but ISA holds well |
| February | 24 | 27 | Output climbing back |
| March | 27 | 28 | Lengthening days |
| April | 28 | 28 | Near peak |
| May | 28 | 28 | Spring peak |
| June | 27 | 27 | Slight heat trim possible |
| July | 26 | 26 | Summer heat |
| August | 26 | 26 | Heat continues |
| September | 26 | 27 | Days shortening |
| October | 25 | 27 | Fall slowdown begins |
| November | 21 | 26 | Lighting gap widens |
| December | 19 | 25 | Minimum without lighting |
ISA Browns barely pause in winter compared with heritage breeds, so the natural-light winter numbers stay relatively high. If you want to top up winter output, add supplemental light to reach 14 to 16 hours total, starting in early September before days shorten. Keep it optional. A natural winter rest can be good for a hard-working hybrid’s long-term health, and the difference for this breed is smaller than it is for most.
Use the feed cost calculator to budget the higher-protein feed these heavy layers need.
What changes the number
The single biggest factor is the hen’s age, followed by feed protein, daylight, heat, and her reproductive health.
Age and laying year
Age is the variable that moves an ISA Brown’s number the most. She lays at a near-constant high rate through years one and two, then output falls about 10 to 15 percent each year after that. Commercial flocks are typically retired around 72 to 76 weeks, right as that decline begins. According to Townline Hatchery figures, a hen-housed ISA Brown averages 321 eggs to 76 weeks of age with an average egg weight of 62.8 grams. Plan your numbers around the first two years and treat anything past that as a bonus.
Feed protein
Layer feed should run 16 to 18 percent protein for this breed, with free-choice oyster shell available at all times. ISA Browns pour so much calcium and protein into eggs that thin shells and a dip in output show up quickly when feed drops below 16 percent. Oyster shell matters most after the first molt, when shell quality naturally starts to slip.
Daylight and coop lighting
Hens need about 14 to 16 hours of light to lay at full rate, and natural daylight falls below that in winter across most of the country. ISA Browns handle this better than nearly any other backyard breed because they barely molt and keep laying through the cold. The natural-light winter dip is real but mild, so supplemental light is genuinely optional for this hybrid rather than close to required.
Heat stress
Laying slows once barn temperatures climb past about 90°F (32°C), when hens eat less and put energy into staying cool. ISA Browns tolerate heat reasonably well, but shade, constant cool water, and airflow keep summer output from sagging. A short heat-driven dip recovers on its own once temperatures ease.
Reproductive health
Because ISA Browns lay so hard, reproductive problems such as egg binding, prolapse, and internal laying become more common after the second year, which is a known trade-off of high-output hybrids. Most live two to three years, though some reach five to eight with attentive care. For an unexplained sharp drop in laying, blood in the nest box, a swollen abdomen, or any sign of illness or injury, consult a licensed poultry veterinarian or your local extension service rather than waiting it out.
How ISA Browns compare
First-year production under normal backyard conditions.
| Breed | Annual eggs | Egg color | Type | Vs ISA Brown |
|---|---|---|---|---|
| ISA Brown | 280–330 | Brown | Hybrid | Baseline |
| Golden Comet | 250–320 | Brown | Hybrid | Similar |
| White Leghorn | 250–320 | White | Production | Similar |
| Rhode Island Red | 250–300 | Brown | Heritage | Lower |
| Buff Orpington | 180–220 | Light brown | Heritage | Lower |
The ISA Brown sits at the very top of the backyard laying chart. By some hatchery estimates it accounts for the majority of the world’s brown egg supply, and almost every other brown layer is measured against it. If your main goal is the most eggs per bird, per dollar of feed, and you want a calm, beginner-friendly hen, this is the pick.
Skip it if you want a long-lived heritage bird, plan to hatch your own replacements, or prefer a flock that lays steadily for five or six years rather than blazing for two. ISA Browns do not breed true, so a pair will not give you more ISA Browns, and their hard-laying bodies tend to wear out sooner than a Buff Orpington or a Wyandotte.
Use the breed selector quiz to compare breeds against your goals and setup.
Frequently asked questions
How many eggs does an ISA Brown lay per year?
An ISA Brown lays about 280 to 330 eggs per year, with roughly 300 being typical for a healthy first-year hen. That is one of the highest figures of any backyard breed, and it holds best through the first two laying years before tapering off.
How many eggs does an ISA Brown lay per week?
A peak ISA Brown lays six to seven eggs per week, which is close to one a day. The rate eases in deep winter and after the second year, but this breed stays more consistent week to week than most.
When do ISA Browns start laying?
ISA Browns usually start laying between 18 and 22 weeks of age, earlier than most heritage breeds. Some hatchery lines begin closer to 16 weeks with good feed and lighting.
Do ISA Browns lay eggs in winter?
Yes, and better than almost any other backyard breed. They barely molt and keep laying through the cold, with only a modest dip when daylight drops below 14 hours, which is why supplemental light is optional for this hybrid.
How long do ISA Browns keep laying?
ISA Browns lay strongly for about two years, then production declines roughly 10 to 15 percent each year afterward. They keep laying occasionally past that, but the high-output window is short by design.
How many eggs will 6 ISA Brown hens lay per year?
Six first-year ISA Brown hens lay about 1,800 eggs per year, or roughly 35 a week, dropping to around 1,500 in year two. Use the eggs per family calculator to match a flock size to how many eggs your household actually uses.
Why did my ISA Brown stop laying?
A pause usually comes down to molt, short winter days, age, or stress, and laying returns once the cause passes. If the stop is sudden and paired with a swollen belly, lethargy, or other illness signs, this breed is prone to reproductive issues, so contact a licensed poultry veterinarian or your local extension service.
Sources: Tractor Supply (tractorsupply.com), Mile Four (milefour.com), Townline Hatchery (via published ISA Brown production records), The Happy Chicken Coop (thehappychickencoop.com). For health concerns about your flock, consult a licensed poultry veterinarian. Last reviewed June 2026.