Pregnancy Calculator
This pregnancy calculator uses your last menstrual period (LMP) and cycle length to estimate your due date with standard medical formulas. It provides your estimated due date, current pregnancy week, trimester, estimated conception date, and a typical fertile window. Based on widely used methods such as Naegele's Rule, this calculator offers simple, quick, and reliable results for early pregnancy tracking. It's ideal for expecting parents who want an easy way to understand their pregnancy timeline without signing up or sharing personal data. All calculations are done privately in your browser and never stored. Whether you're newly pregnant or tracking your progress, this tool gives a clear overview of your pregnancy schedule, including helpful milestones like the end of the first trimester and your anatomy scan date.
First day of your last menstrual period
Default is 28 days. Typical range: 20-40 days.
How It Works
- Due Date: Calculated using Naegele's Rule (LMP + 280 days), adjusted for your cycle length
- Conception Date: Estimated as cycle length - 14 days from LMP
- Fertile Window: Typically 5 days before conception to 1 day after
- Gestational Age: Measured from the first day of your last menstrual period
- Trimester: 1st (0-13 weeks), 2nd (14-27 weeks), 3rd (28+ weeks)
Overview
Calculate your pregnancy due date and track your pregnancy journey with our free Pregnancy Calculator. Whether you're trying to conceive, recently pregnant, or planning ahead, this tool helps you understand your pregnancy timeline. Enter your last menstrual period (LMP) date or due date to see your current gestational age, estimated due date, and key pregnancy milestones. Perfect for tracking your pregnancy progress, planning maternity leave, or preparing for your baby's arrival. All calculations happen in your browser with no data storage for complete privacy.
About
About Pregnancy Calculator
Calculate your estimated due date using your last menstrual period (LMP) and cycle length. Get estimated conception date, pregnancy week, trimester, and key milestones.
Features:
- Calculate due date instantly
- Naegele's Rule formula
- Cycle length customization
- Gestational age tracking
- Trimester identification
- Conception date estimation
- Fertile window calculation
- Key milestone dates
- 100% private - no data stored
FAQ
How accurate is the due date?
The calculator provides an estimate based on Naegele's Rule. Ultrasound dating is more precise, especially early in pregnancy. Only about 5% of babies are born exactly on their due date.
What if my cycle isn't 28 days?
Adjust the cycle length for a more personalized due date. The calculator adds or subtracts days based on the difference from the standard 28-day cycle.
Can I calculate without knowing my LMP?
This calculator requires LMP. If unknown, use an ultrasound-based estimate or consult with your healthcare provider.
What is gestational age?
Gestational age is measured from the first day of your last menstrual period, not from conception. This is the standard medical measurement.
Are results private?
Yes. All calculations stay entirely on your device. We don't collect, store, or transmit any personal data.
What if my gestational age seems wrong?
Verify your LMP date is correct. If you're unsure, an ultrasound can provide a more accurate dating.
Related Tools
What Is a Pregnancy Calculator?
A pregnancy calculator estimates your due date and maps out key milestones — trimester boundaries, screening test windows, and developmental stages — based on the first day of your last menstrual period (LMP) or a known conception date. Standard gestational age counts pregnancy in weeks from LMP, which is typically 2 weeks before actual conception.
A full-term pregnancy lasts approximately 40 weeks (280 days) from LMP, or 38 weeks from conception. The due date calculated by this method is called the Estimated Due Date (EDD). Only about 5% of babies are born on their exact EDD — most births occur within 2 weeks before or after. Gestational age is the standard used by obstetricians worldwide.
How to Use This Pregnancy Calculator
- Enter the first day of your last menstrual period (LMP). This is Day 1 of your cycle.
- Alternatively, if you know your conception date, you can enter that directly (EDD = conception + 38 weeks).
- The calculator shows your estimated due date, current gestational week, trimester boundaries, and key screening windows.
- If an ultrasound has assigned a different gestational age, use that — ultrasound dating (especially before 14 weeks) is more accurate than LMP.
Worked Example: LMP January 1
LMP: January 1 | Cycle length: 28 days | Method: Naegele's Rule
Estimated Due Date: October 8 (LMP + 280 days)
Conception: ~January 14 (Day 14 of cycle)
First trimester ends: March 27 (Week 12)
Second trimester ends: July 10 (Week 27)
Third trimester: July 10 → October 8 (Weeks 28–40)
Viability threshold: ~Week 22–24 (early May)
Full term window: September 17 – October 22 (Weeks 37–42)
Naegele's Rule shortcut: Add 1 year, subtract 3 months, add 7 days to LMP. Jan 1 → Jan 1 + 1yr − 3mo + 7d = Oct 8.
Pregnancy Trimester & Milestone Reference
| Week | Phase | Key Developments | Typical Tests / Actions |
|---|---|---|---|
| 1–4 | Early T1 | Implantation, hCG rises | Home pregnancy test positive by Week 4 |
| 6–8 | T1 | Heartbeat detectable | First ultrasound (dating scan) |
| 10–13 | T1 | Major organs forming, nuchal fold | NIPT/cell-free DNA, nuchal translucency scan |
| 14–20 | T2 | Movement begins, gender visible | Anatomy ultrasound (18–20 weeks) |
| 24–28 | T2/T3 border | Viability improves significantly | Glucose tolerance test (gestational diabetes) |
| 28–32 | T3 | Brain development, lung maturation | Group B strep test (36 weeks) |
| 37–42 | Full term | Baby ready for birth | Weekly cervical checks; induction considered at 41–42 wk |
Full term = 37–42 weeks. Preterm = before 37 weeks. Post-term = after 42 weeks.
Key Concepts: Gestational Age, Trimesters, and Due Date Methods
Gestational age vs. embryonic age. Gestational age (GA) counts from LMP and is used by all medical providers. Embryonic age counts from conception — always 2 weeks less than gestational age for women with 28-day cycles. When your doctor says “you are 8 weeks pregnant,” that means 8 weeks of gestational age from LMP, even though the embryo has only existed for about 6 weeks.
Trimesters. The first trimester (Weeks 1–12) is the highest-risk period — most miscarriages and major structural abnormalities originate here. The second trimester (Weeks 13–27) is often called the “honeymoon trimester” — morning sickness typically subsides, energy returns, and the bump becomes visible. The third trimester (Weeks 28–40+) is rapid growth and preparation for birth.
Due date accuracy. LMP-based dating assumes a 28-day cycle and ovulation on Day 14. For women with irregular cycles or cycles significantly different from 28 days, ultrasound dating is more accurate, especially between 8–14 weeks. An 8-week ultrasound has a margin of error of ±5–7 days; a 20-week ultrasound has a margin of ±10–14 days. Most providers set EDD at the first ultrasound if it differs by >7 days from LMP.
Tips for Tracking Your Pregnancy
Start prenatal care early. Ideally, schedule a first prenatal appointment at 8–10 weeks. Key first-trimester screenings (NIPT, nuchal translucency) are time-sensitive — NIPT can be done as early as Week 10, and nuchal translucency ultrasound must be done between 11 weeks 2 days and 13 weeks 6 days. Missing these windows means waiting for second-trimester anatomy scans.
Take folic acid from conception (or ideally before). 400–800 mcg of folic acid daily, started before pregnancy and continued through the first trimester, reduces the risk of neural tube defects (spina bifida, anencephaly) by 50–70%. These defects form in the first 4 weeks of embryonic development — often before a pregnancy is confirmed. A prenatal vitamin provides this and other essential nutrients.
Know the signs of complications to watch for. In the first trimester: heavy bleeding, severe one-sided pain (ectopic pregnancy), or complete disappearance of symptoms. In the second and third trimesters: decreased fetal movement (after 24 weeks), severe headaches, vision changes, or sudden swelling (preeclampsia signs). When in doubt, call your provider — it is always better to check.
Frequently Asked Questions
How is a due date calculated?
The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. Shortcut: LMP + 1 year − 3 months + 7 days. Early ultrasound (before 14 weeks) is more accurate than LMP-based calculation for women with irregular cycles. The due date produced by first-trimester ultrasound is typically not changed by later scans.
What are the three trimesters of pregnancy?
First trimester: Weeks 1–12 (organ formation, highest miscarriage risk). Second trimester: Weeks 13–27 (rapid growth, anatomy scan, often easier symptoms). Third trimester: Weeks 28–40+ (final growth, birth preparation). The trimester boundaries are based on fetal development stages rather than equal division of the 40-week pregnancy.
When does pregnancy start — at conception or LMP?
Medical convention counts pregnancy from LMP, even though conception occurs roughly 2 weeks later. This is because LMP is known precisely while the exact conception date usually is not. When you are '4 weeks pregnant' by LMP, the embryo is actually about 2 weeks old. The 40-week pregnancy includes these 2 weeks before conception.
What is a full-term pregnancy?
Full term is 37–42 weeks of gestational age. Early term is 37–38 weeks 6 days. Full term is 39–40 weeks 6 days. Late term is 41–41 weeks 6 days. Post-term is 42+ weeks. The American College of OB/GYN (ACOG) discourages elective delivery before 39 weeks unless medically indicated, as the final weeks are important for brain, lung, and liver development.
What does it mean if my due date changes?
Due dates are adjusted based on ultrasound measurements, most commonly from a first-trimester dating ultrasound. If the ultrasound-measured gestational age differs by more than 5–7 days (first trimester) from LMP-based dating, your provider will typically use the ultrasound date. A changed EDD doesn't mean anything is wrong — it just reflects more accurate measurement.
What is the difference between a pregnancy test and a pregnancy calculator?
A pregnancy test (home urine test or blood test) detects hCG hormone to confirm pregnancy is occurring. A pregnancy calculator uses the confirmed pregnancy start date to map out milestones, trimesters, and the due date. Both are useful at different stages: test first to confirm, then use the calculator to track your timeline.
When do pregnancy symptoms start?
Most people notice pregnancy symptoms around 6 weeks — about 2 weeks after a missed period. Common early symptoms: nausea (morning sickness), breast tenderness, fatigue, frequent urination, and food aversions. Implantation bleeding (light spotting) can occur at 10–14 days post-conception. A positive pregnancy test is typically possible 1–3 days after a missed period.
What is viability in pregnancy?
Viability refers to the gestational age at which a baby can potentially survive outside the womb with medical support. The accepted medical threshold is generally 22–24 weeks. At 22 weeks, survival rates with intensive NICU care are around 10–20%. By 24 weeks, survival rates reach 50–70%. By 28 weeks, survival rates exceed 90% with appropriate neonatal care. Fully developed lungs and neurological function continue maturing through Week 37+.