Free Pregnancy Calculator — Estimate Your Due Date & Conception Date
Calculate your estimated due date, conception date, and current pregnancy week instantly. Supports LMP, ultrasound, IVF transfer date, known conception date, and given due date methods.
Calculate Your Pregnancy Details
How to Use This Pregnancy Calculator
Understand the science behind pregnancy dating and conception estimates.
Enter Your LMP Date
Input the first day of your last menstrual period (LMP), which serves as the baseline for most due date calculations.
Select Cycle Length
Enter your average menstrual cycle length for accuracy. The default is 28 days, but you can adjust for shorter or longer cycles.
Get Instant Results
See your estimated conception date, due date, current week, and trimester instantly.
Medical Calculation Method
Our conception date calculator uses Naegele’s Rule—the standard method used in obstetrics. It adds 280 days (40 weeks) to the first day of your last menstrual period, adjusted for your average cycle length. Formula: Due Date = LMP + 280 days - (Cycle Length - 28 days) This approach provides an estimated due date (EDD) that aligns with medical practice and EDD calculators used by healthcare providers.
Formula: Due Date = LMP + 280 days - (Cycle Length - 28 days)
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Understanding Your Pregnancy Results
Pregnancy is measured in gestational weeks starting from your last menstrual period. The conception date typically occurs about two weeks after that, during ovulation.
Key Pregnancy Terms
Gestational Age
The age of your pregnancy measured from the first day of your last menstrual period (LMP).
Estimated Due Date (EDD)
The predicted date of delivery, usually 40 weeks from LMP.
Trimesters
Pregnancy is divided into three stages: first (1–12 weeks), second (13–27), and third (28–40).
Important Considerations
Accuracy Limitations
Only 5% of babies arrive on their exact due date; most come within two weeks before or after.
Irregular Cycles
Women with unpredictable cycles may need ultrasound confirmation for accuracy.
Medical Consultation
Always confirm your EDD and gestational age with your doctor.
First Trimester Dating
Scans between 6–12 weeks provide the most reliable pregnancy dating.
Why Use a Pregnancy Timeline Calculator
Knowing your due date helps track pregnancy progress and plan for key milestones. This pregnancy timeline calculator also identifies trimester transitions, estimated conception date, and major prenatal checkup points.
If your cycles are irregular or you conceived through IVF, you can use this tool along with an IVF transfer due date or early ultrasound for greater precision.
The Formula Explained: Calculate Your Due Date Manually
Verify any EDD by hand using Naegele’s Rule — the same formula obstetricians have relied on for over 200 years.
Naegele’s Rule: LMP Method
Standard Formula (28-day cycle)
Where LMP is the first day of your last menstrual period. 280 days equals 40 weeks — approximately 9 calendar months and 7 days.
Adjusted Formula (variable cycle)
For a 32-day cycle: add 276 days (EDD shifts 4 days later). For a 24-day cycle: add 284 days (EDD shifts 4 days earlier).
Worked Example: LMP = March 1, 2025
Step 1 — Estimated Due Date
March 1 + 280 days = December 6, 2025
Standard 28-day cycle result using Naegele’s Rule.
Step 2 — Estimated Conception Date
March 1 + 14 days = March 15, 2025
Ovulation at day 14 of a standard 28-day cycle.
Step 3 — Trimester Calendar
1st Trimester: Mar 1 – May 24 (weeks 1–12)
2nd Trimester: May 25 – Sep 13 (weeks 13–27)
3rd Trimester: Sep 14 – Dec 6 (weeks 28–40)
Step 4 — 32-Day Cycle Adjustment
Dec 6 + 4 days = December 10, 2025
Longer cycles shift the EDD later by that same number of days.
IVF Due Dates by Embryo Transfer Day
IVF pregnancies are dated from the embryo transfer date because fertilization is a known clinical event. The days added depend on embryo age at transfer:
| Transfer Type | Days to Add | Transfer Date | Example EDD |
|---|---|---|---|
| Day 3 Embryo | 263 days | January 15 | October 5 |
| Day 5 Blastocyst | 261 days | January 15 | October 3 |
| Day 6 Blastocyst | 260 days | January 15 | October 2 |
IVF-based due dates are generally more precise than LMP estimates because ovulation timing is clinically confirmed rather than assumed.
Common Use Cases & Practical Tips
Real scenarios showing how to get the most accurate due date for your specific situation.
Scenario 1: Regular 28-Day Cycle
LMP = April 10. Enter that date with a 28-day cycle. The calculator adds 280 days — EDD = January 15. Estimated conception was around April 24. This is the most straightforward input and matches what your OB will calculate at your first appointment.
Best method: LMP with 28-day cycle
Scenario 2: Irregular Cycle (Varies 25–35 Days)
When your cycle varies significantly, the LMP method may be off by up to 2 weeks. Get a first-trimester ultrasound at 6–10 weeks. The sonographer measures crown-rump length (CRL) within ±5 days of accuracy. Then use the Ultrasound method in this calculator with that gestational age reading.
Best method: First-trimester ultrasound
Scenario 3: Your Doctor Already Gave You an EDD
If your provider said EDD = September 20, select “Due Date” and enter that. The calculator works backward 280 days to estimate your LMP (~December 14 prior year) and conception date (~December 28). This is useful for tracking your current week when you started from an EDD.
Best method: Due Date (reverse calculation)
Scenario 4: IVF Day 5 Blastocyst Transfer
Transfer date = February 1, Day 5 embryo. The calculator adds 261 days → EDD = October 20. This is more precise than LMP dating because egg retrieval and fertilization are clinically confirmed. Your fertility clinic will verify this EDD at your first monitoring scan.
Best method: IVF Transfer Date (Day 5)
Scenario 5: Discovered Pregnancy After Week 8
You know approximately when you conceived — say, March 20. Use Conception Date method. The calculator estimates LMP as ~March 6 and sets EDD around December 11. This gives you a starting point to track your week before your first prenatal scan confirms gestational age.
Best method: Conception Date
Tips for Getting the Most Accurate Result
- •Use a period-tracking app to find your exact LMP — avoid guessing
- •Your first ultrasound overrides LMP dating if they differ by 7+ days
- •Always confirm your EDD with your OB or midwife at your first prenatal visit
- •For irregular cycles, bring 2–3 months of period dates to your first appointment
Pregnancy Week by Week: What to Expect Each Trimester
A trimester-by-trimester overview of fetal development, key prenatal appointments, and what you may experience at each stage.
First Trimester — Weeks 1 to 12
Baby’s Development
- Wks 1–4: Fertilization and implantation; embryo is the size of a poppy seed
- Wk 6: Heartbeat detectable by ultrasound (100–160 bpm)
- Wk 8: Arms, legs, fingers, and toes forming; size of a raspberry
- Wk 10: All vital organs present; embryo becomes a fetus
- Wk 12: Reflexes develop; miscarriage risk drops significantly
What You May Feel
- Nausea and morning sickness (peaks weeks 8–10)
- Extreme fatigue from rising progesterone
- Breast tenderness and sensitivity
- Frequent urination from uterine pressure on the bladder
- Food aversions and cravings beginning
Key Appointments
- Wks 6–10: First prenatal visit and confirmation ultrasound
- Wks 10–13: Nuchal translucency scan (genetic screening)
- Wks 10–12: Blood tests: CBC, blood type, Rh factor, STI screen
Second Trimester — Weeks 13 to 27
Baby’s Development
- Wk 14: Baby can make facial expressions; size of a lemon
- Wk 16: Gender often identifiable; fetal movement begins
- Wk 20: Halfway point; baby is about 10 inches long
- Wk 24: Viability milestone — survival outside the womb possible with medical support
- Wk 27: Eyes open; baby responds to light and sound
What You May Feel
- Nausea typically improves — the “honeymoon trimester”
- First fetal movements (quickening) around weeks 16–22
- Visibly growing baby bump
- Back pain and round ligament pain as the uterus expands
- More energy compared to the first trimester
Key Appointments
- Wks 15–20: Quad screen or cell-free DNA (optional)
- Wks 18–22: Anatomy scan — most detailed ultrasound of pregnancy
- Wks 24–28: Glucose challenge test for gestational diabetes
Third Trimester — Weeks 28 to 40+
Baby’s Development
- Wk 28: Brain develops rapidly; baby practices breathing movements
- Wk 32: Fingernails and hair growing; stores fat for warmth
- Wk 36: Baby typically turns head-down for birth
- Wk 37: Early term — lungs and brain nearly mature
- Wk 40: Full-term; most babies arrive weeks 38–42
What You May Feel
- Braxton Hicks contractions becoming noticeable
- Shortness of breath as the uterus pushes against the diaphragm
- Increased pelvic pressure as baby drops lower
- Difficulty sleeping; frequent urination returns
- “Nesting” instinct — a burst of energy in the final weeks
Key Appointments
- Wks 28–36: Visits every 2 weeks; baby position and growth monitoring
- Wks 35–37: Group B strep swab test
- Wks 36–40: Weekly visits; non-stress test if overdue
- After wk 42: Induction typically recommended
Full-Term Birth Window: Weeks 37–42
Doctors define different birth timing categories, each with distinct clinical implications for your baby’s care:
| Timing | Gestational Age | Clinical Notes |
|---|---|---|
| Preterm | Before 37 weeks | May require NICU support; lung maturity is the primary concern |
| Early Term | 37–38 weeks | Generally healthy; slight increase in breathing and feeding challenges |
| Full Term | 39–40 weeks | Optimal outcomes; brain, lungs, and liver are fully mature |
| Late Term | 41 weeks | Induction may be discussed; monitoring increases |
| Post-term | 42+ weeks | Induction typically recommended; placenta function may begin to decline |
Frequently Asked Questions
Answers to the most common questions about due date calculation, conception timing, and pregnancy tracking
The standard method is Naegele’s Rule: add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle. The adjusted formula is EDD = LMP + 280 days minus (Cycle Length minus 28 days). A 32-day cycle shifts your EDD 4 days later; a 24-day cycle shifts it 4 days earlier. For IVF pregnancies, 266 days are added to the known conception date because fertilization timing is clinically confirmed rather than estimated.
Subtract 266 days from your estimated due date to approximate your conception date. For a standard 28-day cycle, add 14 days to your LMP — that’s roughly when ovulation and conception occurred. For example, if your LMP was March 1, your estimated conception date is March 15 and your EDD is around December 6. Because sperm can survive 3–5 days in the fallopian tubes, the conception date is always an estimate even with this calculation.
Gestational age counts weeks from the first day of your last menstrual period, including the approximately two weeks before conception occurred. Fetal age (embryonic age) starts at the actual fertilization date. At 10 weeks gestational age, the embryo is about 8 weeks old by fetal age. All clinical pregnancy dates — including those from this calculator and from your OB — use gestational age as the standard.
Only 4–5% of babies are born on their exact EDD. Most full-term births occur within two weeks of the estimated date. A first-trimester ultrasound at 6–12 weeks is the most accurate dating method, typically within ±5–7 days. LMP-based calculation is reliable within ±2 weeks for regular 28-day cycles. For irregular cycles, ultrasound dating in the first trimester is always preferred over LMP-based estimates.
IVF due dates are calculated from the embryo transfer date since fertilization is a known clinical event. Add 263 days for a Day 3 embryo transfer, 261 days for a Day 5 blastocyst transfer, or 260 days for a Day 6 transfer. IVF-based EDDs are generally more precise than LMP estimates because there is no need to estimate when ovulation occurred — the fertilization date is documented.
The first trimester spans weeks 1–12. The second trimester covers weeks 13–27 and is often the most comfortable phase because nausea typically improves and energy returns. The third trimester runs from week 28 through week 40 and beyond. Full-term birth is 39–40 weeks, early term is 37–38 weeks, late term is 41 weeks, and post-term is 42 weeks or later. Only about 5% of babies arrive on their exact EDD.
Use the cycle length dropdown in this calculator. The formula automatically subtracts your cycle length minus 28 days from the 280-day standard. A 32-day cycle shifts your EDD 4 days later; a 24-day cycle shifts it 4 days earlier. For cycles that vary by more than 7 days each month, a first-trimester ultrasound is significantly more reliable for gestational dating than any LMP-based calculation.
Full-term is defined as 39–40 completed weeks of gestation. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42 weeks or beyond. Babies born at full term have the best outcomes for brain, lung, and liver development. While births from 37 weeks onward are generally considered medically ready, your provider may discuss induction options if you pass 41 completed weeks without spontaneous labor.
Yes. After entering your dates and clicking Calculate, the tool shows your current gestational week and day, your trimester, and a pregnancy progress bar. It also generates a milestone timeline with heartbeat detection at week 6, anatomy scan window at weeks 18–22, the viability milestone at week 24, and the start of the third trimester at week 28.
Most OBs and midwives recommend scheduling your first prenatal visit between 6 and 10 weeks of pregnancy. This appointment includes pregnancy confirmation, an early ultrasound for accurate gestational dating, blood tests (blood type, Rh factor, CBC, STI screening), prenatal vitamin prescription, and a full due date review. Starting prenatal care early is linked to significantly better outcomes for both you and your baby.