Animal Mortality Rate Calculator
For livestock, poultry and lab-animal cohorts: enter the starting population and the deaths in one period to get the mortality rate, survival rate, annualized mortality, a simple life table and a two-group comparison.
Animals alive at the start of the period, before any deaths.
Life table — projected survivors
Survivors at the start of each period if the measured per-period rate stays constant.
| Month | Survivors | Cumulative deaths | Cohort still alive |
|---|
Group comparison
| Mortality rate | Survival rate |
|---|
Worked example
1,000 broilers, 40 deaths in one month (numbers computed by this tool's own engine):
Mortality rate: 40 / 1,000 x 100 = 4.00% per month
Survival rate: (1,000 - 40) / 1,000 x 100 = 96.00%
Annualized mortality: 1 - 0.9612 = 38.73% per year
Life-table projection (survivors at the start of each month):
| Month | Survivors | Cumulative deaths |
|---|---|---|
| 0 | 1,000 | 0 |
| 1 | 960 | 40 |
| 2 | 922 | 78 |
| 3 | 885 | 115 |
| 6 | 783 | 217 |
| 12 | 613 | 387 |
After one year at this rate, about 613 of the original 1,000 birds remain alive -- the cohort has shrunk by 38.73%.
Formulas used
Mortality rate = deaths / starting population × 100
Survival rate = (starting population − deaths) / starting population × 100 = 100 − mortality rate
Annualized mortality = 1 − (1 − r)n, where r is the per-period mortality as a fraction and n is the number of periods in a year (365 for days, 52 for weeks, 12 for months, 4 for quarters, 1 for years).
Life table: N(t) = starting population × (1 − r)t — survivors at the start of period t.
Relative risk (B vs A) = rateB / rateA; absolute difference is reported in percentage points.
Frequently asked questions
How do you calculate animal mortality rate?
Divide the number of deaths in the period by the starting population and multiply by 100. For example, 40 deaths out of 1,000 birds in one month gives 40 / 1,000 x 100 = 4% per month. The starting population is the count at the beginning of the period, before any deaths occurred.
What is the annualized mortality rate?
It converts a per-period rate into a full-year equivalent, assuming the same per-period risk continues. The formula is 1 - (1 - r)^n, where r is the per-period mortality as a fraction and n is the number of periods in a year. For 4% per month: 1 - 0.96^12 = 38.73% per year. Annualizing lets you compare a monthly rate from one flock with a weekly rate from another on the same scale.
What is the difference between mortality rate and survival rate?
They always add up to 100%. Survival rate = (starting population - deaths) / starting population x 100. With 4% monthly mortality, 96% of the starting cohort survives each month. Mortality rate is used for loss reporting; survival rate is the input most life-table and population-projection models expect.
What is a life table (lx)?
A life table tracks how many animals from a starting cohort are still alive at the start of each period, assuming a constant mortality rate. Starting with 1,000 animals at 4% monthly mortality, the table projects 1,000 alive at month 0, then 960, 922, 885 and so on, down to about 613 alive after 12 months with 387 cumulative deaths. This tool builds that projection forward from your measured rate.
How do I compare mortality between two groups?
Enter both groups and compare two numbers. The absolute difference is in percentage points: 4.00% versus 2.50% is a 1.50-point difference. The relative risk is the ratio of the two rates: 2.50 / 4.00 = 0.625, meaning the second group's mortality is 62.5% of the first group's, or 37.5% lower. Always compare groups measured over the same period length so the comparison is fair.
What is a normal mortality rate for livestock or poultry?
There is no single normal number. Published benchmarks differ widely by species, age group, strain, season and production system -- chick mortality in the first week is tracked separately from grow-out mortality in broilers, and lab mouse colonies use strain-specific baselines. Compare your rate against published figures for your exact species and age group, and treat a rise above your own historical baseline as the signal that matters. When in doubt, consult a veterinarian.
Should culled or sold animals count as deaths?
No. This calculator treats every animal missing from the starting population as a death. If you cull, sell or transfer animals out, subtract those from the starting population first or track them separately, otherwise the mortality rate will be overstated. The same applies to animals added mid-period: use the starting count only, or split the measurement into separate periods.
Why is the annualized rate lower than 12 times the monthly rate?
Because simple multiplication ignores compounding on a shrinking population. At 4% per month, the second month's 4% applies to 960 survivors, not the original 1,000. The annualized formula 1 - (1 - r)^12 accounts for this and gives 38.73%, while 4% x 12 = 48% overstates the true yearly loss.
Can I use this for lab animals or wildlife studies?
Yes. The math is identical for any closed cohort: lab mouse colonies, zebrafish tanks, aquaculture ponds or wildlife study cohorts. For field studies where animals enter and leave the study area freely, use proper capture-recapture estimators instead, because this tool assumes a closed starting population.
Is my data sent anywhere?
No. This calculator runs entirely in your browser using JavaScript. Your population numbers never leave your device, there is no account, and no inputs are tracked. The page works offline once it has loaded.
Free tool by NRTechStudio