Due Date
Estimate your due date with Naegele’s rule, based on the first day of your last period and your cycle length. It also shows how far along you are.
Results update as you type
Formulas use international (WHO) standards — healthy ranges are the same worldwide; only the units differ. The national context below uses U.S. data (CDC / NHANES).
Fertility below replacement
Births per woman. Below 2.1 a population doesn’t replace itself. Source: CDC NCHS.
How the due date is estimated
Naegele’s rule adds 280 days (40 weeks) to the first day of your last period. VitaDup adjusts for your cycle length, since ovulation — and conception — don’t always happen on day 14.
It’s an estimate: only about 4% of babies arrive exactly on the due date. Most come within the two weeks around it.
Trimesters and tracking
Pregnancy splits into three trimesters: first (weeks 1–12), second (13–26) and third (27+). The calculator shows where you are from the weeks elapsed.
A first-trimester ultrasound is the most accurate way to date a pregnancy; this tool is for general guidance.
Frequently asked questions
What if I don’t know my last period date?
The estimate gets less precise. An early ultrasound is the best way to date the pregnancy in that case.
Does it work with irregular cycles?
The cycle-length adjustment helps, but with very irregular cycles the date is less reliable. Check with your provider.
Does this replace prenatal care?
No. It’s informational; pregnancy should always be followed by a healthcare team.
Related calculators
This tool is for general education and is not a substitute for professional medical advice.