Formula Governance
Pregnancy Due Date Calculator — Change Log
Every formula on HealthCalcNow is version-controlled. This page records the formula behind the Pregnancy Due Date Calculator — its current version, the source it comes from, and any revision made since publication.
Current version
Reference. Naegele's Rule (LMP + 280 days); ACOG pregnancy dating guidance
Why this confidence level. LMP-based estimate with high individual cycle variation; the lowest-confidence MVP calculator (only ~5% of births occur on the estimated date).
Revision history
How we version formulas
A calculator's math lives in an isolated module with its own version number. Changing anything that affects a result — a coefficient, a category cutoff, a rounding rule, or the cited source — requires a version bump and an entry on this page. We don't silently edit formulas.
A last-reviewed date is different from a revision: it records when we last checked the formula against its published source and confirmed it still matches. A formula can be reviewed many times without changing.
We take our values from published public-health and scientific sources rather than deriving them ourselves, and we don't claim clinician review that hasn't happened. Read more in our methodology.