Poultry Farms · Guide
Poultry mortality rate: how to calculate it and what's normal by week
Poultry mortality rate is the percentage of birds that died out of the total placed, calculated as (dead birds ÷ birds placed) × 100. Here's the formula with a worked example, a week-by-week table of what's normal versus alarming for broilers, and what to do when your number is too high.
Poultry mortality rate: the formula
Poultry mortality rate is the percentage of birds that died out of the total number placed, calculated as: mortality rate (%) = (number of dead birds ÷ number of birds placed) × 100. So if you placed 5,000 chicks and 150 have died by the end of the batch, your mortality rate is (150 ÷ 5,000) × 100 = 3%.
This is the cumulative mortality rate — the figure used at the end of a batch to judge overall flock performance and compare against your FCR and average body weight. Most farms also track daily mortality (birds dead today ÷ birds alive that morning × 100) and weekly mortality (birds dead that week ÷ birds placed × 100), because a single cumulative number at day 42 hides exactly when the problem happened.
This guide gives you both calculations with worked examples, a week-by-week table of what counts as normal versus alarming for commercial broilers in Indian conditions, the main causes behind each pattern, and when a mortality number should trigger immediate action rather than a note in the register.
Worked example: cumulative and weekly mortality
Take a 5,000-bird broiler batch. Cumulative mortality at day 42: if 165 birds died across the full cycle, that's (165 ÷ 5,000) × 100 = 3.3% — a normal, healthy result for a 42-day broiler cycle in most Indian conditions.
Now break that down by week to see where the deaths actually happened, which is the number that tells you something actionable. Say the mortality was: week 1 — 60 birds, week 2 — 20 birds, week 3 — 10 birds, week 4 — 15 birds, week 5 — 25 birds, week 6 — 35 birds. Weekly mortality rate for week 1 is (60 ÷ 5,000) × 100 = 1.2%, which is within the normal range for early chick losses. But week 6's 35 birds out of the roughly 4,850 still alive is (35 ÷ 4,850) × 100 ≈ 0.72% for that week alone — worth a closer look if your week-6 number is normally under 0.4%, since finishing-age mortality is where heat stress and cardiac events concentrate.
The lesson from this example: a healthy-looking 3.3% cumulative figure can still hide a real problem in week 6 if you never break it down by week. Always calculate both the cumulative number for reporting and the weekly number for diagnosis.
What's a normal mortality rate for broilers by week
Normal mortality is not flat across a batch — it follows a U-shape: higher in the first week as weak chicks are culled by nature, lowest in the middle weeks, and rising again toward the end as birds carry more body weight and heat stress. Use the table below as a general benchmark for commercial broilers in Indian shed conditions; treat your own farm's historical average as the more reliable baseline once you have 5–10 batches of data.
- Week 1: 0.5–1.5% normal. Above 2% suggests chick quality, brooding temperature, or early dehydration issues.
- Week 2: 0.2–0.5% normal. Above 1% suggests early coccidiosis or a ventilation problem.
- Week 3: 0.1–0.3% normal. This is usually the lowest-mortality week of the cycle.
- Week 4: 0.1–0.3% normal. A rise here often points to necrotic enteritis or a feed-change reaction.
- Week 5: 0.2–0.5% normal, rising with body weight and summer heat load.
- Week 6 (finishing): 0.3–0.8% normal in good conditions; can climb well above 1% in a heat-stress or ventilation-failure event.
- Cumulative (full 35–42 day cycle): 2–4% is a good commercial result in Indian conditions; 4–6% is workable but worth investigating; above 6% signals a recurring management, disease, or environmental problem.
What pushes mortality above normal
Three categories account for most above-normal mortality on Indian commercial sheds, and each has a distinct weekly signature you can read off the table above.
Early (week 1–2) spikes usually trace to chick quality at hatch, brooding temperature that's too low or too high, or dehydration if chicks didn't reach water and feed fast enough after placement. Mid-cycle (week 3–4) spikes point toward coccidiosis, necrotic enteritis, or a ventilation problem that built up gradually. Late (week 5–6) spikes are dominated by heat stress and cardiac events — the bird's own body weight and reduced heat tolerance at finishing age make this the highest-risk window for a fan or power failure to turn into a mortality event within an hour. For a fast diagnostic order to work through the moment you see a spike, see our guide to why broilers die suddenly.
Mortality rate and FCR: read them together
Mortality rate alone tells you how many birds you lost; it doesn't tell you whether the birds that survived performed well. A batch with 3% mortality and a poor feed conversion ratio (FCR) is a different problem than a batch with 3% mortality and a good FCR — the first points to a broader stress or disease issue affecting the whole flock, not just the birds that died. Run both numbers together at the end of every batch using our FCR calculator for poultry, and track them side by side over time rather than looking at either number in isolation.
Common mistakes when tracking mortality
The most common mistake is only recording the final cumulative figure and never breaking it down by week — this hides exactly the pattern that tells you what went wrong and when. The second is comparing your farm's mortality against a generic industry number instead of your own historical baseline; a farm that consistently runs 2.5% has a different alarm threshold than one that consistently runs 4.5%, even if both are 'within normal range' on paper. The third is treating a mortality count from the morning round as real-time information — birds that died overnight or during the hottest part of the afternoon are only counted hours after the triggering event, by which point the same condition may have already affected the next batch of birds too.
Catching the cause before the weekly number moves
A mortality rate calculation is always a lagging indicator — it tells you what already happened, not what's happening right now. The gap between a fan tripping at 1 PM and someone noticing dead birds on the 4 PM round is exactly where most preventable mortality occurs, especially in the high-risk finishing weeks. Continuous temperature, humidity, and power-status sensors close that gap by flagging a dangerous condition — a THI crossing 27–28, a fan or power failure — within minutes, with a phone alarm to the shed manager, instead of waiting for the next mortality count to reveal it. See our guide to IoT for poultry farms for how a monitoring system is designed around this, and our poultry monitoring page for the full system overview for broiler and layer sheds.
Talk through your farm's mortality numbers
If your mortality rate is running above what the table above suggests is normal for your shed size and season, book a meeting with the MD to walk through your batch records, your current shed setup, and where a monitoring and alarm system would fit for a farm your size.
Poultry farm monitoring
See how Karuturi Dynamics does this in practice.
FAQ
Frequently asked questions
How do you calculate poultry mortality rate?
Divide the number of dead birds by the number of birds placed, then multiply by 100: mortality rate (%) = (dead birds ÷ birds placed) × 100. For example, 150 dead out of 5,000 placed gives (150 ÷ 5,000) × 100 = 3%. Calculate this both cumulatively (end of batch) and weekly, since the weekly figure shows you when the losses actually happened.
What is a normal mortality rate for broilers?
A cumulative mortality rate of 2–4% across a full 35–42 day broiler cycle is considered a good commercial result in Indian conditions. Week-by-week, expect 0.5–1.5% in week 1, dropping to 0.1–0.3% in the middle weeks, and rising back to 0.3–0.8% in the finishing weeks (5–6) as body weight and heat load increase.
What mortality rate is considered too high for broilers?
A cumulative mortality rate above 5–6% for a standard broiler batch is generally considered high and worth investigating. More important than the cumulative number is where it happened — a spike concentrated in a single week (especially week 1 or the finishing weeks) points to a specific, fixable cause, while a high number spread evenly across the whole cycle suggests a broader management or environmental issue.
How is weekly mortality rate different from cumulative mortality?
Cumulative mortality is total dead birds divided by birds originally placed, calculated at the end of a batch. Weekly mortality is that week's dead birds divided by the number of birds alive at the start of that week, which shows you exactly when in the cycle the losses occurred. A healthy-looking cumulative number can still hide a dangerous spike in one specific week, which is why tracking both matters.
What causes high mortality in the last week of a broiler batch?
Late-cycle (week 5–6) mortality is usually driven by heat stress and cardiac events, because birds at finishing weight have higher body mass and lower heat tolerance than younger birds. A fan or power failure during this window can cause a mortality spike within 30–60 minutes in hot weather, which is why finishing weeks carry the highest risk from any ventilation lapse.
Does mortality rate alone tell you if a batch performed well?
No — mortality rate only measures how many birds you lost, not how well the surviving birds performed. A batch can have acceptable mortality but a poor feed conversion ratio (FCR), which points to a different underlying issue. Track mortality rate and FCR together at the end of every batch to get a complete picture of flock performance.