Mutation Rate Calculator
The expected number of new mutations in a genome each generation from the per-base rate and genome size — and how many accumulate in a lineage over many generations.
Mutation rate per base per generation, times bases in the genome, gives the expected new mutations per offspring.
How the mutation rate calculator works
Mutation rate per base per generation, times bases in the genome, gives the expected new mutations per offspring. For humans, about 1.2 × 10⁻⁸ per base across 3.1 billion bases is roughly 40 to 70 new mutations per child — most in non-coding DNA and nearly all harmless.
Over generations they accumulate linearly, which is the molecular clock: divergence between two lineages is twice the per-generation rate times the generations since they split.
Formula: mutations per generation = rate × genome size; divergence = 2 × rate × generations
Worked examples
| Inputs | New mutations per generation | Note |
|---|---|---|
| The human rate | 37.2 | about 37 per generation |
| A bacterium | 0 | well under one per generation |
| An RNA virus | 3 | several per replication |
FAQFrequently asked questions
How many new mutations does a person have?
About 40 to 70 that neither parent had, from a per-base rate near 1.2 × 10⁻⁸ across three billion bases. The number rises with the father's age.
Are they harmful?
Almost never individually — only about 1.5% of the genome codes for protein, and most changes there are neutral too. It is the rare one in a critical gene that matters.
What is the molecular clock?
The idea that mutations accumulate at a roughly steady rate, so the divergence between two species measures the time since they split.
Why do viruses mutate so fast?
RNA polymerases lack proofreading, so per-base rates are a million times higher. A short genome keeps the count per copy manageable, but it is still several per replication.
Is the rate the same everywhere in the genome?
No — it varies several-fold by region, and CpG sites mutate ten times faster than average. This page uses the genome-wide mean.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- CSIRO — Australia's national science agency
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.