Heritability Calculator
Heritability measures how much of the variation in a trait, within one population and environment, traces back to genetic differences rather than to environment. Breeders, geneticists, and quantitative biologists partition phenotypic variance into genetic and environmental parts to compute broad-sense and narrow-sense heritability. This calculator takes your variance components, returns both heritability ratios, and applies the breeder's equation to predict the response to a chosen selection differential. Enter the variance components you have measured for your population.
Heritability formula
Vg = Va + (Vd + Vi)
Vp = Vg + Ve
Narrow-sense h² = Va / Vp
Broad-sense H² = Vg / Vp
Response to selection R = h² * S
Va is additive genetic variance, the part transmitted reliably to offspring. Vp is total phenotypic variance. The breeder's equation uses narrow-sense heritability because only additive effects predict the offspring response.
Interpreting heritability
- Heritability ranges from 0 to 1 and is specific to the population and environment measured.
- Narrow-sense heritability drives selection response; broad-sense includes dominance and epistasis.
- A larger selection differential or higher heritability produces a larger predicted gain per generation.
- Reducing environmental variance (Ve) raises measured heritability without changing the genetics.
- Heritability within a population does not explain differences between populations or groups.
Heritability: frequently asked questions
What is heritability?
Heritability is the proportion of phenotypic variation in a trait, within a defined population and environment, that is due to genetic variation. Broad-sense heritability (H squared) is total genetic variance divided by phenotypic variance. Narrow-sense heritability (h squared) is the additive genetic variance divided by phenotypic variance, and it is the value that predicts response to selection.
What is the difference between broad-sense and narrow-sense heritability?
Broad-sense heritability H squared = Vg / Vp uses all genetic variance, including dominance and epistatic effects. Narrow-sense heritability h squared = Va / Vp uses only additive genetic variance, the part that parents reliably pass to offspring. Narrow-sense heritability is the relevant quantity for breeders because it predicts how a population responds to selection.
How is phenotypic variance partitioned?
Total phenotypic variance Vp is the sum of genetic variance Vg and environmental variance Ve, so Vp = Vg + Ve. Genetic variance itself partitions into additive (Va), dominance (Vd), and interaction or epistatic (Vi) components: Vg = Va + Vd + Vi. This calculator lets you enter the components you have and computes the heritability ratios from them.
What is the breeder's equation?
The breeder's equation predicts the response to selection: R = h squared times S, where S is the selection differential (the difference between the mean of selected parents and the population mean) and R is the expected change in the offspring mean. It follows directly from narrow-sense heritability and is central to plant and animal breeding.
Does a high heritability mean a trait is genetically fixed?
No. Heritability is a population-and-environment-specific ratio, not a property of an individual or a fixed biological constant. A trait can have high heritability in one population yet differ between populations entirely for environmental reasons. Heritability also says nothing about causes of differences between groups; it only describes variance within the studied population.
Official sources
- National Human Genome Research Institute: NHGRI genetics education.
- U.S. National Library of Medicine: NCBI quantitative genetics literature.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.