Pregnancy Due Date
& Gestational Calculator
Find out exactly how many weeks pregnant you are, your current trimester, and your estimated due date — instantly.
Explore Pregnancy Week by Week
Tap any week to see baby size, milestones & development
Weeks to Months Pregnancy Chart
Complete reference conversion table for pregnancy weeks and months
| Weeks | Month | Trimester |
|---|---|---|
| 1–4 weeks | Month 1 | 1st |
| 5–8 weeks | Month 2 | 1st |
| 9–13 weeks | Month 3 | 1st |
| 14–17 weeks | Month 4 | 2nd |
| 18–21 weeks | Month 5 | 2nd |
| 22–26 weeks | Month 6 | 2nd |
| 27–30 weeks | Month 7 | 3rd |
| 31–35 weeks | Month 8 | 3rd |
| 36–40 weeks | Month 9 | 3rd |
How to Calculate Gestational Age & Due Date
In clinical obstetrics, your gestational age is calculated starting from the first day of your last menstrual period (LMP), rather than the estimated conception date. Because ovulation timing varies and conception is hard to pinpoint, the LMP serves as the universal medical baseline.
Naegele's Rule Formula
The most widely accepted clinical standard for calculating your Estimated Due Date (EDD) is Naegele's Rule: adding 280 days (40 full weeks) to your LMP. Our tool automatically accounts for cycle variations longer or shorter than the standard 28 days.
EDD = First Day of LMP + 280 Days + (Cycle Length - 28 Days)
The Three Trimesters Explained
Weeks 1–13. Critical organogenesis, neural tube formation, heartbeat detection, and embryo-to-fetus transition.
Weeks 14–27. The "golden trimester" of rapid growth, anatomy scans, and feeling the first kicks (quickening).
Weeks 28–40. Rapid weight gain, lung surfactant production, brain maturation, and birth preparation.
Why Don't 40 Weeks Equal Exactly 9 Months?
A standard full-term pregnancy lasts 40 weeks (280 days), which equates to roughly 9 calendar months and 1 week. Because calendar months vary between 28 and 31 days while weeks are always 7 days, tracking pregnancy in weeks offers greater clinical precision.
Ultrasound vs. LMP Calculation
A first-trimester dating ultrasound (crown-rump length measurement) has an error margin of just ±5 days. If the ultrasound date differs by more than 7 days from your LMP calculation, doctors typically update the due date to match ultrasound findings.
Frequently Asked Questions
Common questions regarding pregnancy weeks and due date calculations
Pregnancy weeks (gestational age) are counted from the first day of your last menstrual period (LMP), not from conception. Subtract your LMP date from today's date to get total days, then divide by 7 to determine completed weeks and extra days. Our calculator handles this instantly using Naegele's Rule.
To find out how many weeks pregnant you are, select the first day of your last menstrual period in the calculator above. The tool calculates your exact gestational age, current trimester, and estimated delivery date in real time.
Gestational age is measured from the first day of your last period (LMP). Fetal age (embryonic age) is the actual age of the developing baby, which is typically about 2 weeks less than gestational age because ovulation and fertilization occur roughly 14 days after your period starts.
The standard medical formula is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. If your menstrual cycle is longer or shorter than 28 days, adjust by adding or subtracting the difference.
At 7 months pregnant, you are approximately 28 to 31 weeks along. This marks the beginning of your 3rd trimester.
1st Trimester: Weeks 1 to 13 (organogenesis and foundational development). 2nd Trimester: Weeks 14 to 27 (rapid growth, fetal movements). 3rd Trimester: Weeks 28 to 40+ (lung maturation, brain growth, birth prep).
A first-trimester ultrasound (performed between 7 and 12 weeks) is accurate within ±5 days and can adjust your due date if your LMP is uncertain. After 14 weeks, your LMP-based date remains the clinical benchmark.
Most sensitive home urine pregnancy tests can detect the hCG hormone as early as 10 to 14 days after ovulation — roughly around the time of your missed period (3 to 4 weeks gestational age).