Pedigree Risk Calculator

Work out pedigree risk instantly with clear inputs, formula shown and shareable results.

About Pedigree Risk Calculator

Applies the standard Mendelian recurrence risks for autosomal recessive, autosomal dominant and X-linked recessive patterns.

Formula

Recurrence risks

Autosomal recessive with two carriers: 25% affected, 50% carriers. Autosomal dominant with one affected parent: 50%. X-linked recessive with a carrier mother: 25% of all children, or 50% of sons

Worked example

With the default values below, Pedigree Risk Calculator returns Risk that a child is affected of 25.00%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Inheritance patternone of Autosomal recessive, Autosomal dominant, X-linked recessive: Autosomal recessive
Parental statusone of Both parents carriers, One parent affected, Mother carrier, father unaffected: Both parents carriers
Children plannedaccepts 1–12: 4

Results

Risk that a child is affected: 25.00%
Chance a child is an unaffected carrier: 50.00%
Chance all the children are unaffected: 31.641%
Expected number affected: 1.000

Step by step

1Values used
2Recurrence risks
3Risk that a child is affected= 25.00
4Chance a child is an unaffected carrier= 50.00
5Chance all the children are unaffected= 31.641
6Expected number affected= 1.000

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Do risks reset each pregnancy?

Yes. Each conception is independent, so three unaffected children do not lower the risk for the fourth.

What about incomplete penetrance?

Dominant conditions with reduced penetrance carry a lower observed risk of disease than the 50% transmission risk.