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Carrier Risk Calculator

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

About Carrier Risk Calculator

Combines carrier frequencies for both partners with the one in four recessive transmission risk, and shows the residual risk left by an imperfect carrier test.

Formula

Carrier risk

Risk of an affected child = carrier risk of partner 1 x carrier risk of partner 2 x 0.25; residual risk = carrier frequency x (1 - test detection rate)

Worked example

With the default values below, Carrier Risk Calculator returns Risk of an affected child of 1.00000%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Carrier frequency in the populationaccepts 0–0.5
0.04
Is one partner a known carrierone of Yes, confirmed carrier, No, population risk only
Yes, confirmed carrier
Carrier test detection rateaccepts 50–100
95

Results

Risk of an affected child
1.00000%
Chance both partners are carriers
4.00000%
Residual carrier risk after a negative test
0.20000%
Expressed as odds
About 1 in 100

Step by step

  1. 1Values used
  2. 2Carrier risk
  3. 3Risk of an affected child= 1.00000
  4. 4Chance both partners are carriers= 4.00000
  5. 5Residual carrier risk after a negative test= 0.20000
  6. 6Expressed as odds= About 1 in 100

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 or fees or charges into account.
  • Figures are rounded for display to 5 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

Why does a negative test leave residual risk?

No panel detects every variant, so a negative result reduces but never eliminates carrier probability.

Does ancestry change the frequency?

Substantially. Carrier frequencies for cystic fibrosis, thalassaemia and Tay-Sachs vary widely between populations.

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