Pregnancy Due Date Calculator — Accurate & Free
Use this free pregnancy due date calculator to find your estimated due date, current pregnancy week, trimester, days remaining, and baby development milestone — all in one place. Supports LMP, Conception Date, and IVF Transfer methods.
Pregnancy Due Date Calculator
Select your calculation method and enter your date to get your estimated due date, pregnancy week, trimester, and more.
Important Medical Disclaimer
→ This pregnancy due date calculator provides estimates only and is not a substitute for professional medical advice.
→ Due dates are estimates — only about 5% of babies are born on their exact due date. Always follow your healthcare provider’s advice.
→ If you have any concerns about your pregnancy, consult your doctor or midwife immediately.
→ Sources: medplore.com, nhs.uk, whattoexpect.com, americanpregnancy.org, perinatology.com
How is Your Pregnancy Due Date Calculated?
A pregnancy due date calculator estimates when your baby will be born based on the start of your last menstrual period (LMP), conception date, or IVF transfer date. The standard method — used by doctors worldwide — is Naegele’s Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period.
The 280-day calculation is based on an average 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, this pregnancy due date calculator adjusts the estimate accordingly using your cycle length input.
The three calculation methods
- Last Menstrual Period (LMP) — the most common method. Add 280 days to the first day of your last period. Adjusted for cycle length differences from 28 days.
- Conception Date — if you know when you conceived, add 266 days. This is equivalent to LMP + 280 days assuming ovulation on day 14.
- IVF Transfer Date — for Day 5 embryo transfer, add 261 days. For Day 3 transfer, add 263 days. The IVF due date calculator accounts for the embryo age at the time of transfer.
How Accurate is a Pregnancy Due Date Calculator?
A pregnancy due date calculator gives an estimated due date (EDD) — not a guaranteed birth date. Research shows that only about 4–5% of babies are born on their exact due date. Most babies are born within two weeks before or after the EDD, and a birth anywhere between 37 and 42 weeks is considered normal.
Factors that affect accuracy
- Irregular periods — women with irregular cycles may have less accurate LMP-based estimates.
- Uncertain dates — if you are unsure of your LMP, an early ultrasound (before 12 weeks) is more accurate.
- First-trimester ultrasound — the most accurate way to confirm a due date, especially when LMP is uncertain.
- IVF pregnancies — IVF due dates are more precise because the exact fertilisation date is known.
Once your first-trimester ultrasound is done, your healthcare provider may adjust your due date based on the baby’s measured size. This updated date becomes your official EDD.
Pregnancy Week by Week — Trimester Guide
Pregnancy is divided into three trimesters, each with distinct developmental milestones for the baby and changes for the mother. The pregnancy due date calculator above identifies which trimester you are currently in.
| Trimester | Weeks | Baby Development | Mother’s Experience |
|---|---|---|---|
| 1st Trimester | Weeks 1–13 | All organs form, heartbeat starts, baby reaches 8cm | Morning sickness, fatigue, breast tenderness |
| 2nd Trimester | Weeks 14–26 | Baby moves, senses develop, growth accelerates | Energy improves, baby bump visible, movements felt |
| 3rd Trimester | Weeks 27–40 | Rapid weight gain, lungs mature, baby positions for birth | Back pain, frequent urination, Braxton Hicks contractions |
Key pregnancy milestones by week
| Week | Milestone |
|---|---|
| Week 6–8 | First heartbeat detectable by ultrasound |
| Week 10–12 | Nuchal translucency (NT) scan for Down syndrome screening |
| Week 12 | End of first trimester — miscarriage risk significantly reduced |
| Week 18–20 | Anatomy scan (anomaly scan) to check baby’s development |
| Week 24–28 | Glucose tolerance test (gestational diabetes screening) |
| Week 28 | Third trimester begins — appointments become more frequent |
| Week 36 | Group B strep (GBS) swab test in many countries |
| Week 37 | Baby considered full term — lungs mature |
| Week 40 | Estimated due date |
| Week 41–42 | Post-term — discuss induction with healthcare provider |
Why Due Dates Can Change
It is very common for a due date calculated from LMP to be revised after the first ultrasound. This happens because the ultrasound measures the baby’s actual size — which is a more accurate indicator of gestational age than the date of the last period.
- Irregular ovulation — if you ovulated later or earlier than day 14, the LMP-based estimate will be off.
- Uncertain LMP — many women cannot remember the exact date of their last period.
- Multiple pregnancies — twins and triplets often have different growth rates, affecting dating.
- IVF pregnancies — the fertilisation date is known exactly, so the due date from IVF transfer is more precise and rarely changes.
If your ultrasound due date differs from your LMP due date by more than 7 days in the first trimester, your doctor will typically use the ultrasound date as the official EDD.
Sources & References
→ NHS (UK) — How your due date is calculated: nhs.uk/pregnancy
→ American Pregnancy Association — Pregnancy Due Date Calculator
→ ACOG (American College of Obstetricians and Gynecologists) — Methods for Estimating Due Date
→ Medplore, WhatToExpect.com, Perinatology.com — Calculation methodology reference