Free Pregnancy Due Date Calculator Online
Calculate your estimated due date by last menstrual period, conception date, ultrasound, or IVF transfer date. Includes a visual trimester timeline, week-by-week milestones, and a dog pregnancy due date calculator.
Personalized Pregnancy Due Date Estimator — 5 Methods
Not a one-size-fits-all calculator. Choose from five evidence-based methods to estimate your pregnancy due date — including dedicated IVF and dog pregnancy modes.
Last Menstrual Period (LMP)
Uses Naegele's Rule — adds 280 days (40 weeks) to the first day of your last period. Adjusts automatically for cycle lengths shorter or longer than 28 days.
IVF Transfer Date
Calculates your due date from the embryo transfer date — supporting both Day-3 embryo (+263 days) and Day-5 blastocyst (+261 days) transfers for clinical-grade accuracy.
Visual Trimester Timeline
See exactly where you are in your pregnancy with a visual progress bar, trimester breakdown, and week-by-week milestone cards showing key developmental events.
Dog Pregnancy Calculator
Estimate your pregnant dog's due date based on the mating date. Uses the standard 63-day canine gestation period with a whelping window of 58–68 days.
Calculate Your Pregnancy Due Date in 3 Steps
Select Your Method
Choose from Last Menstrual Period, Conception Date, Ultrasound, IVF Transfer, or Dog Pregnancy. Each tab adapts the inputs to that specific calculation method.
Enter the Date
Input the relevant date using the date picker. For LMP, also set your average cycle length. For IVF, select Day-3 or Day-5 embryo. For ultrasound, enter weeks and days.
See Your Due Date & Timeline
Instantly view your estimated due date, current gestational age, trimester, days remaining, and a visual pregnancy timeline with developmental milestones.
What Makes This Pregnancy Due Date Calculator Stand Out
5 Calculation Methods
LMP with adjustable cycle length, conception date, ultrasound-based, IVF transfer (Day-3 & Day-5), and dog pregnancy — all in one tool.
Week-by-Week Tracker
See exactly how many weeks and days into your pregnancy you are, which trimester you're in, and how many days remain until your estimated due date.
IVF-Specific Support
Built for IVF patients with precise Day-3 embryo (+263 days) and Day-5 blastocyst (+261 days) calculations based on your actual transfer date.
Visual Pregnancy Timeline
A trimester progress bar with milestone cards showing key developmental events — from first heartbeat detection to full-term readiness.
Dog Pregnancy Mode
Calculate your pregnant dog's due date using the 63-day average canine gestation, with a whelping window range of 58–68 days.
100% Private
All calculations happen in your browser. No health data is collected, stored, or transmitted anywhere. No registration required.
How This Pregnancy Due Date Calculator Compares
| Feature | WebToolTrix | Calculator.net | WhatToExpect | BabyCenter | NHS |
|---|---|---|---|---|---|
| LMP + Cycle Length Adjustment | ✓ | ✓ | ✓ | ✓ | ✗ |
| Conception Date Method | ✓ | ✓ | ✗ | ✗ | ✗ |
| Ultrasound-Based Calculation | ✓ | ✓ | ✗ | ✗ | ✗ |
| IVF Transfer (Day-3 & Day-5) | ✓ | ✓ | ✗ | ✗ | ✗ |
| Visual Trimester Timeline | ✓ | ✗ | ✗ | ✗ | ✗ |
| Week-by-Week Milestones | ✓ | ✗ | ✓ | ✓ | ✗ |
| Dog Pregnancy Calculator | ✓ | ✗ | ✗ | ✗ | ✗ |
| No Account Required | ✓ | ✓ | ✗ | ✗ | ✓ |
| 100% Browser-Only (No Data Sent) | ✓ | ✗ | ✗ | ✗ | ✗ |
Understanding Pregnancy Due Date Calculations
Everything you need to know about estimating your pregnancy due date — from Naegele's Rule and conception dating to IVF-specific formulas and canine gestation.
How Pregnancy Due Dates Are Calculated by Last Menstrual Period
The most widely used method to predict a pregnancy due date is based on the last menstrual period (LMP). This approach, formalized as Naegele's Rule, adds 280 days (40 weeks) to the first day of your last period. It assumes a standard 28-day menstrual cycle with ovulation occurring on day 14.
The formula is straightforward: Due Date = LMP + 280 days. If your cycle is longer than 28 days, ovulation likely occurs later — and the due date shifts accordingly. For example, a 35-day cycle would shift the estimated due date 7 days later than a 28-day cycle. This is why our pregnancy due date calculator includes an adjustable cycle length from 21 to 40 days.
According to the American College of Obstetricians and Gynecologists (ACOG), the LMP-based method remains the standard first step in pregnancy dating, though it should ideally be confirmed with an early ultrasound.
Pregnancy Due Date by Date of Conception
If you know the exact date of conception — or the date of ovulation — you can calculate your pregnancy due date by adding 266 days (38 weeks) from that date. This method is more precise than LMP because it eliminates the guesswork about when ovulation occurred.
The difference between LMP and conception methods is approximately 14 days: LMP adds 280 days from the period start, while conception adds 266 days from fertilization — both targeting the same estimated delivery date. Knowing your conception date is especially useful for women with irregular cycles or those who track ovulation using basal body temperature or ovulation predictor kits.
Calculating Due Date from Ultrasound
An early ultrasound — ideally performed between 8 and 12 weeks — is considered the most accurate method for dating a pregnancy. The sonographer measures the embryo's crown-rump length (CRL) and compares it to standardized growth charts to determine gestational age.
To calculate the due date from an ultrasound: Due Date = Ultrasound Date − Gestational Age + 280 days. For example, if an ultrasound on January 15 shows a gestational age of 10 weeks and 3 days, the calculator back-calculates the LMP equivalent date and projects 280 days forward.
ACOG recommends that if the ultrasound-based due date differs from the LMP-based date by more than 5–7 days in the first trimester, the ultrasound date should take precedence.
Pregnancy Due Date Calculator for IVF — Day-3 vs. Day-5 Embryo Transfer
For women undergoing in vitro fertilization (IVF), the due date calculation is inherently more precise because the exact date of embryo transfer is known. The formula depends on the embryo's age at the time of transfer:
- Day-3 embryo transfer: Due Date = Transfer Date + 263 days
- Day-5 blastocyst transfer: Due Date = Transfer Date + 261 days
These formulas work because a full-term pregnancy is 266 days from conception. Since a Day-3 embryo has already developed for 3 days, you subtract 3 from 266 to get 263 days from the transfer date. Similarly, a Day-5 blastocyst yields 266 − 5 = 261 days.
This method of calculating an IVF pregnancy due date is recommended by the CDC's ART (Assisted Reproductive Technology) guidelines. Your fertility clinic will typically confirm this estimate with a first-trimester ultrasound.
How Accurate Are Pregnancy Due Date Predictions?
No due date calculation is perfectly precise. Research shows that only about 5% of babies are born on their exact estimated due date. The majority of births occur within the two-week window surrounding the due date:
- Early term: 37 weeks 0 days through 38 weeks 6 days
- Full term: 39 weeks 0 days through 40 weeks 6 days
- Late term: 41 weeks 0 days through 41 weeks 6 days
- Post-term: 42 weeks 0 days and beyond
Factors that can affect accuracy include irregular menstrual cycles, uncertain LMP dates, the timing of ovulation within the cycle, and individual biological variation. First-trimester ultrasound dating is generally accurate to within ±5–7 days.
Pregnancy Due Date Timeline: Trimester Milestones
Understanding your pregnancy timeline helps you track your baby's development and plan for prenatal care. A pregnancy calendar divides the 40-week journey into three trimesters, each with distinct developmental milestones:
| Trimester | Weeks | Key Milestones |
|---|---|---|
| First Trimester | Weeks 1–12 | Implantation, heartbeat detection (~6 wk), major organ formation, morning sickness peaks (8–10 wk) |
| Second Trimester | Weeks 13–26 | Gender visible on ultrasound (~18 wk), quickening/first kicks (~20 wk), viability milestone (~24 wk) |
| Third Trimester | Weeks 27–40 | Eyes open (~28 wk), lung development accelerates (~34 wk), baby drops into pelvis (~36 wk), full term (~39 wk) |
Tracking your pregnancy due date week by week allows you to prepare for key prenatal appointments, screenings (like the glucose tolerance test at 24–28 weeks), and the approaching delivery date.
NHS Pregnancy Due Date Calculator vs. Naegele's Rule
The NHS pregnancy due date calculator uses essentially the same underlying method as Naegele's Rule — adding 280 days to the first day of the last menstrual period. However, the NHS version often does not adjust for non-standard cycle lengths, which can make it less accurate for women with cycles shorter than 25 or longer than 30 days.
Our calculator improves on this by allowing you to set your specific cycle length from 21 to 40 days, automatically adjusting the ovulation offset. This provides a more personalized pregnancy due date prediction aligned with ACOG's clinical recommendations.
Tracking Your Pregnancy Due Date Week by Week
Once you have your estimated due date, counting backward tells you your current gestational week. Here's what "gestational age" means:
- Gestational age starts counting from the first day of your LMP — not from conception. This means you're technically "2 weeks pregnant" at the moment of conception.
- Fetal age counts from conception and is typically 2 weeks less than gestational age.
Your healthcare provider schedules prenatal visits based on gestational weeks. Key appointments typically occur at 8, 12, 16, 20, 24, 28, 32, 36, and 38–40 weeks. The 20-week anatomy scan is particularly important for checking fetal development and may adjust your pregnancy due date if measurements differ significantly from the LMP-based estimate.
Dog Pregnancy Due Date Calculator: Canine Gestation Period
For breeders and pet owners, knowing a pregnant dog's due date is essential for planning proper prenatal veterinary care and preparing for whelping. The average canine gestation period is 63 days from the date of ovulation or mating.
Key facts about dog pregnancy:
- Average gestation: 63 days from mating/ovulation
- Normal range: 58–68 days (varies by breed and litter size)
- Whelping window: Prepare supplies between days 58–63
- Veterinary check: Ultrasound confirmation at ~25 days; X-ray for puppy count at ~45 days
If your dog has not delivered by day 67–68, contact your veterinarian immediately. Small breeds tend to deliver slightly earlier (around 60 days), while large breeds may go closer to 65 days. The American Kennel Club (AKC) recommends monitoring the dam's temperature — a drop below 100°F typically signals labor within 24 hours.
When to Consult Your Healthcare Provider
While a pregnancy due date calculator provides a helpful estimate, it should never replace professional medical guidance. Contact your OB-GYN or midwife:
- To confirm your due date with a first-trimester ultrasound
- If your cycle is highly irregular, making LMP-based dating unreliable
- If you experience complications like bleeding, severe pain, or signs of preterm labor
- If you are past 41 weeks and have not begun labor
- For any IVF pregnancy — your fertility specialist should confirm the due date at your first ultrasound
Frequently Asked Questions About Pregnancy Due Dates
The most common method is Naegele's Rule — add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle. If your cycle is longer or shorter, the due date adjusts accordingly. Other methods include conception date (+266 days), ultrasound dating, and IVF transfer date calculations.
Only about 5% of babies are born on their exact due date. Most deliveries occur within 2 weeks before or after the estimate. First-trimester ultrasound dating is accurate to ±5–7 days. LMP-based calculations are less precise if your cycle is irregular.
Naegele's Rule is the standard formula for estimating pregnancy due dates. Named after German obstetrician Franz Naegele, the rule adds 280 days (40 weeks) to the first day of the last menstrual period. It assumes ovulation on day 14 of a 28-day cycle. Most healthcare providers and pregnancy due date calculators — including the NHS calculator — use this as their baseline method.
For IVF pregnancies, the formula depends on the embryo's age at transfer. For a Day-3 embryo, add 263 days to the transfer date. For a Day-5 blastocyst, add 261 days. These are more precise than LMP-based calculations because the exact date of embryo creation is known.
A Day-3 embryo (cleavage-stage) has developed for 3 days after egg retrieval. A Day-5 embryo (blastocyst) has developed 2 additional days. Day-5 transfers are more common because blastocysts have higher implantation rates. For due date calculation, the 2-day difference means Day-5 transfers result in a due date 2 days earlier than Day-3 transfers from the same transfer date.
Yes. Your healthcare provider may adjust your due date after the first ultrasound, especially if the measurements differ from the LMP-based estimate by more than 5–7 days. The due date may also be revised if the baby is measuring significantly ahead or behind in later ultrasounds, though first-trimester dating is most reliable.
The average pregnancy lasts 280 days (40 weeks) from the first day of the last menstrual period, or 266 days (38 weeks) from conception. Full-term is defined as 39 weeks 0 days through 40 weeks 6 days. Most babies arrive between 37 and 42 weeks.
If you know your exact conception or ovulation date, add 266 days (38 weeks) to that date. This is equivalent to adding 280 days from the LMP minus the 14-day ovulation offset. Use this method if you track ovulation with basal body temperature or ovulation predictor kits.
Dogs are typically pregnant for 63 days (about 9 weeks) from the date of mating or ovulation. Normal canine gestation ranges from 58 to 68 days depending on breed, litter size, and the exact timing of fertilization. Your veterinarian can confirm the pregnancy with an ultrasound around day 25.
Add 63 days to the date of mating or breeding. The expected whelping window is days 58–68. Prepare your whelping box by day 55 and watch for signs of labor — nesting behavior, restlessness, and a temperature drop below 100°F. Use the Dog mode in our calculator above for an instant estimate.
Trimesters are divided as follows: First trimester — weeks 1 through 12; Second trimester — weeks 13 through 26; Third trimester — weeks 27 through 40. Enter your date in the calculator above to see your exact trimester, current week, and days remaining until your due date.
100% browser-based. All calculations happen entirely in your browser. No pregnancy-related data is collected, transmitted, or stored on any server. No registration or account is required.