Due Date Tool
Estimate your pregnancy due date using your last menstrual period, cycle length, conception date, ultrasound dating or IVF embryo transfer. Explore gestational age, trimester, remaining days, pregnancy progress and estimated milestone dates in one place.
| Milestone | Gestation | Date | Status |
|---|
For planning only. Due dates are estimates, not a prediction of the day of birth. Your maternity clinician may use ultrasound dating or other clinical information to confirm or revise your due date.
Table of Contents
Highlights
- Four dating methods: last period, conception, ultrasound and IVF
- Adjustable menstrual cycle length and reference date
- Estimated due date, gestational age and trimester at a glance
- Interactive pregnancy progress timeline and milestone status table
- Export estimated milestones to CSV, calendar, JSON or HTML
How Due Date Tool Works?
Pregnancy dating conventionally counts 40 weeks (280 days) from the first day of the last menstrual period (LMP), rather than from fertilisation. The tool first derives an estimated gestational start date according to the selected input method, then adds 280 days.
| Input method | Estimated gestational start date |
|---|---|
| Last period | First day of LMP + (usual cycle length − 28 days) |
| Conception | Estimated conception date − 14 days |
| Ultrasound | Scan date − (weeks at scan × 7 + extra days) |
| IVF transfer | Transfer date − (14 + embryo age in days) |
For example, an LMP of 9 July 2026 with a 28-day cycle gives an estimated due date of 15 April 2027. A 35-day cycle moves this estimate seven days later. The IVF option supports embryos aged 3, 5, 6 or 7 days at transfer.
Gestational age is the number of days between the estimated gestational start and the selected reference date, expressed in completed weeks and additional days. Days remaining equal the due date minus the reference date. Progress is the elapsed gestational days divided by 280, capped between 0% and 100%. The first trimester covers weeks 0–13, the second weeks 14–27, and the third begins at week 28.
The timeline also marks estimated dates for 12 weeks, 20 weeks, 37 weeks and the due date, showing whether each milestone is upcoming, today or passed relative to the reference date.
Practical Use Cases
People tracking periods: Enter the first day of the last menstrual period and usual cycle length to see an initial estimated due date and current gestational age.
People who know their conception date: Use an estimated fertilisation date to view a 40-week pregnancy timeline without relying on the last menstrual period.
People with ultrasound dating: Enter the scan date and the gestational weeks and days reported at the scan to explore a due date based on that measurement.
IVF patients: Enter the embryo transfer date and embryo age at transfer to estimate pregnancy dating for a day-3, day-5, day-6 or day-7 embryo.
Expectant parents planning appointments: Review trimester boundaries and 12-, 20- and 37-week milestones, then export the milestone dates as a CSV or calendar file.
Partners and support people: Select a reference date to see the gestational age, time remaining and a visual progress timeline for planning ahead.
Accuracy and Limitations
All dates are estimates based on a standard 280-day gestation. The last-period method adjusts for cycle length but assumes ovulation shifts in step with that length; irregular cycles or uncertain period dates can make it inaccurate. Conception dates may be uncertain, and ultrasound estimates depend on the gestational age supplied, without accounting for scan-specific measurement uncertainty. IVF dating assumes the chosen embryo age and transfer date are correct. Trimester boundaries and milestone dates are fixed planning conventions, not personalised clinical predictions. Birth commonly occurs before or after the estimated due date, and a maternity clinician may revise dating using clinical information.
