Advanced Due Date Calculator
Example Data Table
| Method | Sample Input | Formula Basis | Best Use |
|---|---|---|---|
| Last period | LMP: 2026-01-01, Cycle: 28 days | LMP + 280 days | Regular cycles with known period date |
| Conception | Conception: 2026-01-15 | Conception + 266 days | Known ovulation or conception timing |
| Transfer | Day 5 transfer: 2026-01-20 | Transfer + 261 days | Assisted reproduction cycles |
| Ultrasound | 8 weeks, 3 days on scan date | Scan date + remaining days to 280 | Dating from measured gestational age |
Formula Used
The calculator uses pregnancy dating formulas based on a 40 week gestational pregnancy. It estimates the due date from the selected source date.
- Last period: Estimated ovulation = LMP + cycle length - luteal phase. Due date = ovulation + 266 days.
- Standard 28 day cycle: Due date = LMP + 280 days.
- Conception: Due date = conception date + 266 days.
- Embryo transfer: Due date = transfer date + 266 days - embryo age.
- Ultrasound: Due date = scan date + 280 days - gestational age in days.
- Digital weeks estimate: Due date range is estimated from the test date and displayed weeks range.
These formulas are planning estimates. Confirm important pregnancy dates with a qualified care provider.
How To Use This Calculator
- Select the dating method that matches your best information.
- Enter the required date and any optional details.
- Use cycle length and luteal phase for a better period-based estimate.
- Press the calculate button.
- Review the due date, trimester, gestational age, and milestones.
- Download the CSV or PDF report after results appear.
About This Calculator
About This Calculator
A Clearblue due date calculator helps estimate the likely birth date using common pregnancy dating methods. The result is an estimate, not a fixed appointment. Many babies arrive before or after the calculated date.
Date Sources
The calculator above supports several inputs. You can use the first day of the last period. You can also use a known conception date, an ovulation date, an embryo transfer date, a scan age, or a digital weeks estimate. This makes the tool useful when one date is unknown or less reliable.
Pregnancy is usually counted from the first day of the last menstrual period. In a typical 28 day cycle, ovulation happens around day 14. The due date is then about 280 days after the period start. For longer or shorter cycles, the calculator adjusts ovulation by using the cycle length and luteal phase.
Conception based dating uses 266 days from the estimated conception date. Transfer based dating subtracts embryo age from the normal conception to birth interval. Ultrasound dating uses the scan date and the measured gestational age on that day.
Why Results Can Change
The result also shows gestational age today. This helps you see the current week and day. It also estimates trimester, days remaining, key milestone dates, and a possible delivery window. These details can support planning, but they should not replace medical advice.
Due dates can shift after an early ultrasound. Cycle variation, late ovulation, irregular periods, assisted reproduction, and uncertain test timing can all affect the estimate. The most accurate dating is usually discussed with a qualified clinician.
Export And Review
Use the chart to compare milestones. Download the CSV when you need spreadsheet records. Download the PDF when you want a simple report for printing or sharing. Always confirm important pregnancy dates with your doctor, midwife, or local care provider.
It is helpful to save the method you used. A due date from a period may differ from one based on a scan. A transfer date may be more exact for assisted cycles. Keep notes beside each result. Review them during your first visit.
Discuss the strongest date source with your care team.
FAQs
1. Is this calculator a medical diagnosis?
No. It gives an estimate based on common pregnancy dating formulas. Always confirm important dates with your doctor, midwife, or qualified care provider.
2. Which method is usually most accurate?
Known embryo transfer dates and early ultrasound dating are often stronger sources. Period-based estimates can be affected by cycle length and ovulation timing.
3. Why does cycle length matter?
A longer cycle may mean later ovulation. A shorter cycle may mean earlier ovulation. The calculator adjusts period-based dating using cycle length and luteal phase.
4. What does gestational age mean?
Gestational age counts pregnancy from the estimated first day of the last period. It is usually about two weeks more than conception age.
5. Can a due date change?
Yes. A clinician may update the date after an early scan, irregular cycle review, fertility treatment details, or other medical information.
6. What is the delivery window?
The delivery window shown here runs from 37 to 42 weeks. It is a planning guide, not a promise of when birth will happen.
7. Can I use a digital weeks estimate?
Yes. The calculator gives a broad range from the test date and weeks shown. This method is less exact than clinical dating.
8. What should I download?
Use CSV for spreadsheet records. Use PDF for a simple printable report. Keep the method and input date with every saved result.