Pregnancy Calculator
Track gestational age in weeks and days, current trimester progress, and upcoming milestone dates based on your last period.
Calculate current gestational age in weeks and days, trimester stage, and key developmental scan dates based on your last menstrual period.
See also: Due Date Calculator, TDEE Calculator (Total Daily Energy Expenditure), 1RM Calculator (One-Rep Maximum)
How it is calculated
Gestational Age = Days since LMP ÷ 7; Estimated Due Date (EDD) = LMP + 280 Days
Worked example: LMP on June 15 with Standard 28-Day Cycle
First day of last period: June 15, 2026. Standard 28-day cycle length.
- Count elapsed days from June 15 to current date (Oct 24) = 131 days.
- Divide by 7 to determine gestational weeks: 131 ÷ 7 = 18 weeks and 5 days.
- Determine trimester: 18 weeks falls into the Second Trimester (weeks 13 to 26).
- Add 280 days to LMP to calculate EDD: June 15 + 280 days = March 22, 2027.
18 Weeks, 5 Days pregnant with an Estimated Due Date of March 22, 2027.
How to Use This Calculator (Step-by-Step)
- Select the first day of your last normal menstrual period (LMP).
- Adjust your average cycle length if your typical menstrual cycle is shorter or longer than 28 days.
- Review your exact week-by-week progress and estimated due date.
Frequently asked questions
How accurate is a pregnancy calculator?
Calculators provide estimates based on Naegele’s rule. Only about 4% to 5% of babies arrive on their exact estimated due date; most arrive within two weeks before or after.
When is the 12-week dating scan usually scheduled?
In standard obstetric care (like the NHS), the formal dating ultrasound is scheduled between 11 weeks and 14 weeks of gestational age.
Why is pregnancy counted from my last period rather than conception?
Obstetricians and midwives date pregnancy from the first day of the last period, known as gestational age, which is roughly two weeks before ovulation and conception. That is why the formula divides days since the last period by seven.
What if my cycle is not 28 days?
Enter your own average cycle length, which the input accepts between 21 and 45 days. The standard 28-day cycle is only the default, and a shorter or longer cycle changes the gestational age and estimated due date.
What milestone information does the calculator show?
It shows gestational age in weeks and days, current trimester progress, and upcoming milestone dates based on your last period, including the estimated due date and key developmental scan dates described in the page summary.
Is the estimated due date exact?
No. The estimate uses the standard 280-day rule from the last period, and calculations are estimates only, not medical advice or diagnosis. Consult an obstetrician or midwife for medical guidance about your pregnancy.