Calculator Inputs
Example Data Table
| Method | Example Inputs | Sample Gestational Age | Sample Fetal Age | Sample Due Date |
|---|---|---|---|---|
| LMP | LMP: Jan 1, 2026, cycle: 30, luteal: 14, calculation: Mar 23, 2026 | 11 weeks 4 days | 9 weeks 4 days | October 9, 2026 |
| Conception | Conception: Jan 20, 2026, calculation: Mar 23, 2026 | 10 weeks 6 days | 8 weeks 6 days | October 13, 2026 |
| Ultrasound | Scan: Feb 15, 2026, scan age: 8w 3d, calculation: Mar 23, 2026 | 13 weeks 4 days | 11 weeks 4 days | September 25, 2026 |
Formula Used
1. Gestational age from an equivalent LMP: Gestational Age = Calculation Date − Equivalent LMP Date.
2. Fetal age from conception: Fetal Age = Calculation Date − Estimated Conception Date.
3. Due date from conception: Estimated Due Date = Conception Date + 266 days.
4. Equivalent LMP from due date: Equivalent LMP = Estimated Due Date − 280 days.
5. Ultrasound dating: Current Gestational Age = Ultrasound Age at Scan + Days Since Scan.
6. IVF dating: Estimated Conception = Transfer Date − Embryo Age in Days.
Standard obstetric dating usually counts about 14 days before conception as gestational age. Real clinical dating may be adjusted by your healthcare team.
How to Use This Calculator
- Select the dating method that matches your information.
- Enter the relevant dates or scan age details.
- Choose the calculation date to view age on that day.
- Click the calculate button to show results above the form.
- Review gestational age, fetal age, due date, trimester, and milestones.
- Use CSV or PDF export if you want a copy.
Frequently Asked Questions
1. What is fetal age?
Fetal age usually measures the baby’s age from conception. It is commonly about two weeks less than gestational age, which starts from the menstrual timeline.
2. What is the difference between fetal age and gestational age?
Gestational age starts from the pregnancy dating baseline, often LMP. Fetal age starts closer to conception. That is why fetal age is often around 14 days shorter.
3. Which method is usually most reliable?
Early ultrasound and IVF transfer dating are often very reliable. LMP can also work well when cycle timing is regular and dates are known accurately.
4. Why do cycle length and luteal phase matter?
They help estimate ovulation more accurately. Longer or shorter cycles can shift conception timing, which changes fetal age and due date estimates.
5. Can I use this for IVF or frozen embryo transfer?
Yes. Choose the IVF method, enter the transfer date, and select embryo age. The calculator then estimates conception, gestational age, and due date from transfer timing.
6. Why can scan-based results differ from LMP-based results?
Ovulation may not happen on the same day each cycle. Ultrasound measures development directly, so providers may prefer scan-based dating when results conflict.
7. Is the due date exact?
No. A due date is an estimate, not a guarantee. Many healthy births happen before or after that day within a normal delivery window.
8. Should I use this instead of medical advice?
No. This tool is for planning and education. Please confirm pregnancy dating, scans, and clinical decisions with a qualified healthcare professional.