Due Date Calculator
Calculate your baby's due date using 4 methods — LMP, conception date, IVF transfer, or ultrasound weeks. Compare methods side by side and see which one to trust.
4
METHODS
±5-7d
ULTRASOUND ACCURACY
37-42w
FULL-TERM WINDOW
Choose Your Calculation Method
📌 Due date = LMP + 280 days, adjusted for cycle length and luteal phase
👶 Estimated Due Date
April 3, 2027
196 days to go
- Gestational Age
- 12w 0d
- Trimester
- 1st
- Baby's Sign
- ♈ Aries
🤰 Pregnancy Progress
30%
complete
Week 12 of 40
⏳ Countdown to Due Date
28
Weeks
0
Days
0
Hours
0
Mins
🌱
First Trimester
Weeks 1-13
🌸
Second Trimester
Weeks 14-27
🎀
Third Trimester
Weeks 28-40
📐 Due Date — All 4 Methods Compared
| Method | Estimated Due Date |
|---|---|
| LMP (Naegele's Rule) | April 3, 2027 |
| Conception Date | April 3, 2027 |
| IVF Transfer (Day 5 (Blastocyst)) | April 8, 2027 |
| Ultrasound Dating | March 6, 2027 |
How Due Dates Are Calculated — And Why the Method Matters
A due date isn't measured directly — it's estimated backward from a known reference point using the length of an average pregnancy: 40 weeks (280 days) from the first day of your last menstrual period, or 38 weeks (266 days) from conception. The reference point you use changes the math, and some reference points are more reliable than others. That's the whole reason a due date calculator needs four separate methods rather than one formula.
🧮 The 4 Calculation Methods
1. LMP (Naegele's Rule): Due = LMP + 280 days, adjusted by (cycle length − 28) and (luteal phase − 14)2. Conception Date: Due = Conception + 266 days (38 weeks) | assumed LMP = Conception − 14 days3. IVF Transfer: Due = Transfer date + 263 days (Day 3) | + 261 days (Day 5) | + 260 days (Day 6)4. Ultrasound (Crown-Rump Length): Due = Scan date + (280 − gestational age in days at scan)🩸
LMP — Best for Regular Cycles
Naegele's Rule works well if your cycles are consistently close to 28 days with a typical luteal phase. It's the default method because it needs no medical testing, but it's also the least precise when cycles run long, short, or irregular.
📍
Conception Date — Best with Known Ovulation
If you've been charting basal body temperature, using ovulation predictor kits, or tracking a fertility app closely, a known or estimated conception date removes the cycle-length guesswork entirely.
🧪
IVF Transfer — Most Precise
With assisted reproduction, the embryo's exact age at transfer is a clinical fact, not an estimate — making IVF-based due dates about as accurate as a dating method gets, on par with an early ultrasound.
🔍
Ultrasound — Best for Irregular Cycles or Unknown LMP
When your last period date is unreliable, irregular, or unknown (common with PCOS or after stopping hormonal birth control), a first-trimester ultrasound measurement is the most trustworthy fallback.
What to Expect Near Your Due Date
📊
Only ~4-5% Born On Time
Only about 4-5% of babies are born on their exact calculated due date. Roughly 70-80% are born within two weeks before or after. Due dates are estimates, not appointments.
⏰
Full Term vs. Post-Term
Full term is 39w0d-40w6d. Early term is 37w0d-38w6d. Late term is 41w0d-41w6d. Post-term is 42w0d+, when induction is typically discussed with your provider.
🔍
Ultrasound Accuracy Window
A first-trimester ultrasound (8-14 weeks) is accurate to about ±5-7 days. After 20 weeks accuracy drops to roughly ±2-3 weeks, so an early scan carries more weight than a later one.
📅
Plan for a Window, Not a Date
Rather than fixating on a single day, think of your due date as the center of a 5-week window (roughly 37-42 weeks). Aim to have practical preparations complete by week 36.
— FAQ