NIPT PPV and Residual Risk Calculator

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Interpret one NIPT result for trisomy 21, trisomy 18 or trisomy 13 using an age-based starting chance or the prior chance on your report.

This is a screening estimate for one selected condition, not a diagnosis or an overall pregnancy-outcome estimate.

NIPT result probability estimate

For singleton pregnancies. Choose one condition and one NIPT result.

For a donor-egg pregnancy, use the egg provider’s age when the eggs were retrieved. The published age table covers ages 15 to 50, with a narrower range for trisomy 13.

NIPT is a screening test. A high-risk result is not a diagnosis, and a low-risk result does not reduce the chance to zero.
Test performance settings

Defaults come from SMFM Consult Series #74. Replace them only if your laboratory provides values for the same condition and pregnancy type.

Peer-Reviewed Science
Updated Dec 2025
See Methodology
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What the result means

A high-risk NIPT result means the selected condition is more likely. It does not confirm the diagnosis. A low-risk result means the condition is less likely, but false-negative results can occur. The calculator uses the same predictive-value equations used in genetic counselling: the starting chance, sensitivity, and specificity all affect the result.

The age-based starting chances are population estimates at about 16 weeks. If your report includes a prior chance based on ultrasound, biochemical screening, or medical history, use the custom option instead.

Why this is not a "chromosomally normal baby" calculator

Standard NIPT mainly screens for trisomy 21, trisomy 18, and trisomy 13. Some tests offer additional screening, but no NIPT panel checks every chromosome difference, genetic condition, or structural problem. A result for one condition cannot establish that every chromosome is normal.

Live birth is a separate outcome. For an estimate that combines pregnancy outcome and chromosome risk, use the Live Birth and Chromosome Risk Calculator.

Considering CVS or amniocentesis?

Use the CVS or Amniocentesis After NIPT Calculator to compare procedure-related loss with estimated diagnostic yield after your NIPT result.

Important limits

  • This version is for singleton pregnancies.
  • It covers trisomy 21, trisomy 18, and trisomy 13 only.
  • It does not use fetal fraction, ultrasound findings, a previous affected pregnancy, or a parental chromosome rearrangement unless those factors are already reflected in a custom prior chance.
  • A no-result NIPT is not calculated as a low-risk result.
  • Do not use this page to make a testing or pregnancy decision without discussing the actual laboratory report with an obstetric clinician or genetic counselor.

Sources and calculation method

The default sensitivity and specificity values come from SMFM Consult Series #74: Cell-free DNA screening for aneuploidies, endorsed by ACOG in 2025. The age-based prior chances and predictive-value formulae use the public Genetic Support Foundation NIPT Predictive Value Calculator. That resource describes its prevalence figures as estimates at 16 weeks.

Clinical interpretation follows ACOG's January 2026 screening guidance.

Last method review: 12 July 2026. This calculator is educational and is not a diagnosis or medical recommendation.