Pregnancy Calculator
Track current gestational age, developmental trimesters, and vital milestones week by week.
Parameters & Inputs
Summary & Breakdown
Trimester Timeline Milestones
About the Pregnancy Calculator
Gestational progress in clinical obstetrics is officially calculated from the first day of your last normal menstrual period (LMP), meaning a full-term pregnancy spans 40 weeks (280 days).
This pregnancy calculator details exactly how far along you are today, which trimester you are in, and provides the projected calendar dates for your critical developmental scans.
Adjusting for menstrual cycles longer or shorter than 28 days ensures precision.
How the Calculations Work
Calculates days elapsed between the LMP date and today to determine completed weeks and days. Applies Naegele's rule adjusted for cycle length to establish the 40-week due date.
Days Along = Today - LMP | Due Date = LMP + 280 days + (Cycle Days - 28)
Variables & Definitions
- LMP: First day of the last normal menstrual cycle
- 280 days: Standard 40 gestational weeks
- Cycle adjustment: Adds or subtracts days if cycle differs from the 28-day standard
If LMP was 100 days ago, gestational age is 100 / 7 = 14 weeks and 2 days. The mother has entered the second trimester (weeks 14 through 27).
Key Terms Explained
Gestational Age
Age of the pregnancy measured in completed weeks from the start of the last menstrual period.
Trimesters
The three physiological stages: 1st (weeks 1-13), 2nd (weeks 14-27), and 3rd (weeks 28-40+).
Anatomy Scan
Comprehensive mid-pregnancy ultrasound typically scheduled between weeks 18 and 22.
Full Term
A baby delivered between 39 weeks 0 days and 40 weeks 6 days is considered full term.
Practical Tips & Pitfalls to Avoid
Confirm with early dating ultrasound
A first-trimester crown-rump length ultrasound provides the most accurate clinical dating.
Start prenatal vitamins with folate
400-800 mcg of folic acid daily supports neural tube development in early pregnancy.
Track kick counts in third trimester
Starting around week 28, monitoring fetal movement patterns provides reassurance.
Stay hydrated throughout pregnancy
Drinking 8-10 glasses of water daily supports expanding amniotic fluid volume and blood plasma.
Frequently Asked Questions
Most women know the date their period started, but exact ovulation and fertilization timing varies. Obstetrics universally benchmarks from LMP.
Standard gestation is 280 days, or 40 weeks, or approximately 9 months and 1 week.
Only about 4% to 5% of babies arrive on their exact calculated due date; most arrive within two weeks before or after.
The second trimester officially begins at week 14 (13 weeks and 1 day).
If a first-trimester ultrasound differs from your LMP date by more than 7 days, your obstetrician will adjust your official due date.