Pregnancy Due Date Calculator by Conception
Plan and track your pregnancy with precision. Our pregnancy due date calculator by conception uses the exact date of conception to estimate your due date, current gestational age, and time remaining — all in one friendly dashboard. Whether you are confirming a positive test, syncing with your OB-GYN, or simply curious about milestones, this free pregnancy calculator gives you accurate results instantly.
How Pregnancy Dating Works
| Method | Basis | Accuracy |
|---|
| Conception date | Exact fertilization date | Most accurate |
| Last menstrual period (LMP) | 2 weeks before conception | Standard clinical baseline |
| IVF transfer date | Known embryo age | High for assisted pregnancies |
| Ultrasound dating | Fetal measurements | Most accurate at 8-14 weeks |
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- free pregnancy calculator — no signup required
- gestational age calculator — weeks and days pregnant
- pregnancy week calculator — track weekly milestones
The 280-Day Rule
A full-term pregnancy is 280 days (40 weeks) from the first day of the last menstrual period, or 266 days (38 weeks) from conception.
| Milestone | From LMP | From Conception |
|---|
| Ovulation | ~Day 14 | Day 0 |
| Fertilization | ~Day 14 | Day 0 |
| Implantation | ~Day 20 | Day 6 |
| First heartbeat | ~Day 42 | Day 28 |
| First movements | ~Day 98 | Day 84 |
| Full term | ~Day 280 | Day 266 |
Trimester Breakdown
| Trimester | Weeks (from LMP) | Weeks (from conception) | Key Developments |
|---|
| First | 1-12 | 0-10 | Organogenesis, morning sickness |
| Second | 13-27 | 11-25 | Quickening, anatomy scan |
| Third | 28-40 | 26-38 | Rapid growth, birth prep |
Weekly Size Reference
| Week | Fruit Size | Length | Weight |
|---|
| 4 | Poppy seed | 0.04 in | 0.04 oz |
| 8 | Raspberry | 0.6 in | 0.04 oz |
| 12 | Lime | 2.1 in | 0.5 oz |
| 16 | Avocado | 4.6 in | 3.5 oz |
| 20 | Banana | 6.5 in | 10.5 oz |
| 24 | Corn | 8.7 in | 1.3 lb |
| 28 | Eggplant | 10.9 in | 2.2 lb |
| 32 | Squash | 11.4 in | 3.8 lb |
| 36 | Papaya | 13.3 in | 5.8 lb |
| 40 | Watermelon | 20.1 in | 7.5 lb |
Common Questions
| Question | Answer |
|---|
| Why 280 days from LMP? | Adds 2 weeks before conception |
| Can I use this for IVF? | Yes — use embryo transfer date |
| What if dates differ? | Ultrasound at 8-14 weeks is most accurate |
| Are all pregnancies 40 weeks? | 38-42 weeks is normal |
| What is gestational age? | Age from LMP, not conception |
Calculation Formula
1. Take conception date
2. Add 266 days (38 weeks)
3. Result = estimated due date
4. Current gestational age = today minus conception date
5. Remaining = due date minus today
Best Practices
| Practice | Why |
|---|
| Use ultrasound dating early | Most accurate before 14 weeks |
| Track LMP if conception unknown | Provides baseline estimate |
| Note IVF transfer date | Use for assisted pregnancies |
| Confirm with provider | Clinical validation matters |
| Expect a range | Due dates are estimates, not deadlines |
Conclusion
Our pregnancy due date calculator by conception gives you a clear, accurate estimate from the moment of fertilization. Whether you need a simple due date calculator, a gestational age tracker, or a pregnancy week calculator with milestones, this tool supports your journey with data and compassion. Calculate now and plan ahead with confidence.