Life Table Survivorship Calculator

Enter the initial cohort count followed by the survivors recorded at later ages, and the calculator divides every count by the initial cohort size. The result includes age, number surviving, survivorship as a proportion, and survivorship as a percentage, making cohorts of different starting sizes easier to compare without changing the original observations.

Prepare survivor counts in age order

Begin with a cohort whose members are followed through successive age classes. Enter the number alive in the first class first, then add the count alive in each later class in chronological order. The initial value must be greater than zero because it supplies the denominator for every survivorship calculation. Counts must be whole, nonnegative numbers, and they must stay the same or decrease as age advances. A cohort life table tracks the same original group, so an increase would normally indicate that observations from another cohort were added, that an age class was entered out of sequence, or that the values represent something other than survivors. Repeated counts are valid and indicate that no recorded deaths occurred across that interval. A final zero is also valid. Use start age to identify the age attached to the first observation and age interval to describe evenly spaced classes, such as yearly, five-year, or half-year intervals. Keep all ages in one consistent unit and document that unit with your analysis because the output deliberately preserves numeric ages without guessing whether they represent days, months, or years.

Understand the survivorship calculation

For each age class x, age-specific survivorship is calculated as l_x = n_x / n_0, where n_x is the number of cohort members alive at that age and n_0 is the initial cohort size. The first row therefore always has survivorship 1, or 100 percent. Every later result lies between zero and one because a closed cohort cannot gain members. For example, if 760 members remain from an initial 1,000, survivorship is 0.76 and the displayed percentage is 76. This is a proportion of the original cohort, not a conditional probability of surviving only the preceding interval. That distinction matters: interval survival would divide one age-class count by the count immediately before it, whereas this calculator always uses the initial count as the denominator. Values are rounded only to remove floating-point noise and remain precise enough for ordinary demographic, ecological, and laboratory life tables. The output retains the original survivor counts beside the normalized values, so readers can verify the denominator, distinguish small samples from large ones, and reproduce each calculation directly.

Interpret and compare the resulting life table

Read down the life table to see how the original cohort is retained across age. A gradual decline indicates that losses are spread across many classes, while a sharp step identifies an interval before which a large share of the original cohort disappeared. A flat segment means that the recorded number surviving did not change. Because survivorship is normalized to the initial cohort, two cohorts with different starting sizes can be compared on the same proportional scale. Comparisons are most meaningful when their age origins, age intervals, inclusion rules, and observation methods match. The calculation does not correct for migration, missed observations, censoring, sampling error, or individuals that enter after the cohort begins. It also does not estimate mortality hazards or life expectancy; those require additional assumptions and, often, information about deaths or person-time within intervals. Treat the table as a transparent transformation of supplied counts rather than an inferential model. Before publishing a comparison, inspect unexpected increases in the source data, confirm that zero counts are genuine, retain the cohort-size field, and state the age unit so another reader can understand exactly what each row represents.