Pregnancy Due Date Calculator
The Pregnancy Due Date Calculator helps you estimate when your baby will arrive using the most common clinical methods: last menstrual period (LMP), conception date, ultrasound measurement, or IVF transfer date. Enter your information to get a precise estimated due date (EDD), your current gestational age, trimester, and important pregnancy milestones. The tool applies Naegele's Rule and clinically accepted pregnancy dating guidelines, adjusting calculations automatically based on your cycle length or ultrasound results. All calculations are private and run directly in your browser. Perfect for early pregnancy planning, scheduling appointments, or exploring timelines for prenatal care.
Last Menstrual Period
How It Works
- LMP: Uses Naegele's Rule (LMP + 280 days). Cycle length adjusts ovulation.
- Conception: Due date = conception + 266 days.
- Ultrasound: Derives LMP from ultrasound date and GA, then calculates EDD.
- IVF: Adjusts embryo age to conception equivalent, then calculates EDD.
Overview
Use this pregnancy due date calculator to estimate your expected due date, current gestational age, trimester, and pregnancy milestones using the most common dating methods. It supports last menstrual period, conception date, ultrasound dating, and IVF transfer timing, which makes it more useful than a simple single-input due date estimate. This page is designed to help you understand pregnancy timing clearly while keeping the result private and easy to review.
About
About Pregnancy Due Date Estimation
Pregnancy dating is usually an estimate built from the best available timing information. Different methods are useful in different situations, so this tool supports the common calculation paths clinicians and patients reference most often.
Features:
- LMP-based due date estimation using Naegele's Rule
- Conception-date calculation for known conception timing
- Ultrasound-based dating support
- IVF and embryo-transfer due date support
- Gestational age, trimester, and milestone tracking
- Private browser-based calculation with printable results
Which dating method is usually best?
If you have a reliable LMP, that is often the first estimate people use. If cycle timing was unusual or uncertain, an early ultrasound is often considered more accurate. For assisted reproduction, IVF transfer details usually provide the clearest timeline because the embryo age is known more precisely.
FAQ
What does this calculator estimate besides the due date?
It also helps you see gestational age, trimester timing, important milestones, and the full-term window so the result is more useful for planning.
Why can different methods give slightly different due dates?
They use different timing assumptions. LMP relies on cycle timing, ultrasound relies on fetal measurement-based dating, and IVF uses known transfer timing, so the estimates can vary a bit.
Is ultrasound dating usually more accurate than LMP?
Early ultrasound is often the most precise dating method when cycle timing is uncertain, especially in the first trimester.
Does this replace advice from a doctor or midwife?
No. It is a planning and estimation tool. Clinical dating and prenatal guidance should still come from your healthcare provider.
Related Tools
What Is a Pregnancy Due Date Calculator?
A pregnancy due date calculator estimates your expected delivery date (EDD) based on the first day of your last menstrual period (LMP) or a known conception date. The standard calculation uses Naegele's rule: add 280 days (40 weeks) to the LMP. This assumes a 28-day cycle with ovulation on day 14 — adjustments are needed for cycles that differ significantly from this baseline.
Your due date is an estimate, not a deadline. Only about 4% of babies are born on their exact EDD. Full-term births typically occur between 39–41 weeks, and anything between 37–42 weeks is generally considered normal. The calculator also shows your current gestational week, trimester, and key milestone dates throughout the pregnancy.
How to Use the Due Date Calculator
- Enter the first day of your last menstrual period (LMP) — this is the most common input method.
- Alternatively, enter a known conception date if you tracked ovulation precisely.
- Adjust cycle length if yours differs from the default 28 days.
- The calculator returns your EDD, current gestational week, trimester, and milestone dates.
- Cross-reference with your healthcare provider's dating scan for the most accurate EDD.
Worked Example: Calculating Due Date from LMP
Using Naegele's rule with a standard 28-day cycle:
LMP: June 1, 2024
EDD calculation: June 1 + 280 days = March 8, 2025
Trimester 1 ends: ~September 7, 2024 (week 13)
Trimester 2 ends: ~December 21, 2024 (week 26)
Full term range: February 22 – March 22, 2025 (weeks 39–41)
For a 30-day cycle, add 2 days to all dates. For a 35-day cycle, add 7 days.
Pregnancy Timeline Reference
| Milestone | Gestational Week | Key Development |
|---|---|---|
| First missed period | ~Week 4 | hCG detectable; home test positive |
| First trimester ends | Week 13 | Organ formation complete; miscarriage risk drops significantly |
| Anatomy scan | Week 18–20 | Detailed ultrasound; gender determination possible |
| Viability threshold | Week 24 | Survival outside womb possible with intensive NICU support |
| Second trimester ends | Week 26 | Lungs developing; eyes begin to open |
| Early term begins | Week 37 | Baby considered early term; most organ systems mature |
| Full term begins | Week 39 | Optimal developmental readiness for birth |
| Post term begins | Week 42 | Increased monitoring; induction often recommended |
Key Concepts: How Due Dates Are Calculated and Confirmed
Naegele's rule. The standard due date formula was developed by German obstetrician Franz Karl Naegele in the early 19th century: take the first day of the LMP, subtract 3 months, and add 7 days (equivalent to adding 280 days). This rule assumes a 28-day cycle and that pregnancy lasts exactly 40 weeks from the LMP. It remains the global standard despite being based on limited 19th-century data, primarily because it's simple and performs reasonably well for most women with regular cycles.
Ultrasound dating. An early ultrasound (8–12 weeks) measures the crown-rump length (CRL) and assigns a gestational age accurate to ±5–7 days. This is more accurate than LMP-based dating for women with irregular cycles. The 20-week anatomy scan can date to ±10–14 days. If the ultrasound date and LMP date differ by more than 7 days (first trimester) or 14 days (second trimester), most providers revise the EDD based on the ultrasound.
Why most babies aren't born on their due date. Only ~4% of births occur on the EDD. The mean delivery date is approximately 40 weeks 5 days for first-time mothers (slightly earlier for subsequent pregnancies). Labour can begin due to fetal lung maturity signals, uterine stretching, hormonal cascades, and other factors that are not yet fully understood. The EDD is the midpoint of a 5-week window (37–42 weeks) during which birth is considered normal.
Tips for Using Your Due Date Effectively
Plan around a window, not a date. Arrange maternity leave, baby shower, and preparation to be complete by week 37–38 rather than your exact EDD. Many first-time mothers go past their due date by 5–10 days. Planning for “the baby will arrive sometime in this 3-week window” reduces anxiety and prevents over-reliance on a specific date that is unlikely to be exact.
Track your gestational weeks, not just the due date. Your healthcare provider will monitor development by gestational week, not by countdown to due date. Understanding which week you're in helps you track prenatal appointment timing (first appointment typically 8–10 weeks, anatomy scan 18–20 weeks, Group B Strep test 35–37 weeks, weekly checks after 36 weeks) and fetal development milestones.
Keep your LMP date recorded accurately. The LMP is used for dozens of clinical decisions throughout pregnancy — screening test result interpretation, kick count benchmarks, decision-making around preterm labour, and induction timing. If you don't know your exact LMP, tell your provider and rely on early ultrasound dating instead. Estimates based on uncertain LMP dates can affect important clinical thresholds.
Frequently Asked Questions
How accurate is a due date calculator?
LMP-based due date calculations are accurate to within about ±2 weeks for women with regular 28-day cycles. For irregular cycles, accuracy decreases significantly. Early ultrasound (8–12 weeks) is accurate to ±5–7 days and is the gold standard for due date confirmation. Most providers establish the official EDD at the first dating scan rather than relying solely on LMP calculation.
What if my due date changes after an ultrasound?
It's common for the EDD to be revised after an early ultrasound, especially if your cycle length differs from 28 days or if you're unsure of your LMP date. A revision of ±7 days in the first trimester is routine and doesn't indicate any problem. The revised date based on crown-rump length measurement is generally more accurate than calendar calculation.
What is the difference between LMP and conception date?
LMP (last menstrual period) is the first day of your last period — used as the starting point for gestational age counting. Conception typically occurs ~14 days after LMP. Due date from LMP = LMP + 280 days. Due date from conception = conception date + 266 days (38 weeks). Both should yield the same EDD when ovulation occurred on day 14 of a 28-day cycle.
What week is considered full term?
The American College of Obstetricians and Gynecologists (ACOG) defines: Early term = 37–38 weeks, Full term = 39–40 weeks, Late term = 41 weeks, Post term = 42+ weeks. The 39–40 week window is when the baby's brain, lungs, and liver are most fully developed for birth. Elective induction before 39 weeks is generally avoided unless medically indicated.
How long is a full-term pregnancy?
A full-term pregnancy lasts 40 weeks (280 days) from the LMP, or approximately 38 weeks from conception. This is often described as 9 months, though it's actually closer to 9.2 calendar months. The 3-trimester framework divides pregnancy into: Trimester 1 (weeks 1–13), Trimester 2 (weeks 14–26), Trimester 3 (weeks 27–40+).
What is post-term pregnancy and when is induction recommended?
Post-term pregnancy is defined as ≥42 weeks gestation. After 41–42 weeks, the placenta may begin to age and lose function, increasing risks of fetal distress and stillbirth. Most providers offer elective induction between 41–42 weeks. Induction before 42 weeks is not universally recommended but may be offered at 40–41 weeks in low-risk pregnancies after discussion of individual risk factors.
Can my due date change multiple times?
Yes. The due date may be revised at the first ultrasound (most common), at the 20-week anatomy scan (if there's a significant discrepancy), or if there's evidence of fetal growth restriction or accelerated growth. Multiple EDD revisions are normal and reflect increasingly accurate information about fetal size and development.
Does cycle length affect my due date?
Yes. If your cycle is longer than 28 days, you likely ovulate later, meaning conception occurred later than day 14 — and your actual due date may be later than the LMP-based calculation. For a 35-day cycle, add 7 days to the standard calculation. For a 21-day cycle, subtract 7 days. This tool applies these cycle-length adjustments automatically when you enter a non-standard cycle length.