Introduction
This Pregnancy Calculator estimates a 40-week pregnancy timeline from five common starting points: the first day of your last menstrual period, an existing due date, ultrasound dating, a known conception date, or an IVF embryo transfer date. It helps you translate one reliable date into a full schedule that includes current pregnancy week, trimester, estimated conception timing, and practical milestone windows.
How to Use
Choose the dating method that matches the information you have. Enter the required date fields, then review the pregnancy summary as of the reference date. If you use ultrasound dating, enter both the scan date and the gestational age reported on that scan. If you use IVF, choose the embryo age at transfer. The result is an estimate only and should not replace clinician-confirmed dating.
Features
- •Five dating methods in one tool: LMP, due date, ultrasound, conception date, and IVF transfer
- •Current pregnancy week and day, trimester, progress, estimated conception date, and estimated LMP
- •Milestone windows for early dating ultrasound, anatomy scan, glucose screening, Group B strep screening, and term timing
- •Cycle-length adjustment for LMP-based estimates and embryo-age handling for IVF dating
- •Local browser-based calculation with no account or upload required
Which Dating Method Is Best?
In routine pregnancy dating, the first day of the last menstrual period (LMP) is the traditional starting point, with an estimated due date set 280 days later. That works well when cycles are reasonably regular and the date is known clearly. A known conception date works differently because pregnancy dating counts about 266 days from conception rather than 280 days from LMP.
Ultrasound dating is especially important when cycle dates are uncertain or when the scan suggests a different gestational age than expected. Early ultrasound is generally more accurate for pregnancy dating than later ultrasound. For IVF pregnancies, transfer date plus embryo age creates a strong timeline anchor because fertilization timing is more controlled than in spontaneous conception cycles.
How to Read the Schedule
The calculator converts your input into an estimated gestational age, shown in weeks and days, and maps it to a trimester. It also estimates the likely LMP date, the approximate conception date, and the number of days remaining until the due date. The trimester cards summarize the broader pregnancy stages, while the milestone list highlights common prenatal planning windows.
These milestone windows are not guarantees. They are best understood as planning ranges for commonly timed visits or screening discussions, such as a detailed anatomy ultrasound in mid-pregnancy or gestational diabetes screening later in the second trimester.
Important Medical Limits
Pregnancy dating can change after clinical review. If your clinician updates your due date after reviewing an early ultrasound or fertility treatment details, follow that medical record rather than the calculator. This tool is designed for education and planning, not diagnosis, and is most appropriate for a singleton pregnancy. Irregular cycles, uncertain conception timing, twins, or complicated IVF timing should be reviewed with a clinician.
Seek urgent medical attention for severe pain, heavy bleeding, leaking fluid, trouble breathing, fainting, or decreased fetal movement later in pregnancy. Those situations require clinical care, not date estimation.
Which Dating Input Should You Use?
Choose the input that best matches the information you already have.
| Method | Formula used in the calculator | Best use case |
|---|---|---|
| Last menstrual period | LMP + 280 days, with optional cycle-length adjustment | Regular or fairly predictable cycles with a known last period date |
| Existing due date | Uses the due date as the anchor and back-calculates the schedule | You already have a clinician-confirmed or previously estimated due date |
| Ultrasound | Scan date + remaining days to 40 weeks based on gestational age on scan | Cycle dates are uncertain or scan-based dating is available |
| Conception date | Conception date + 266 days | Conception timing is known closely |
| IVF transfer | Transfer date + (266 - embryo age in days) | Embryo transfer date and embryo age are known |
Typical Milestone Windows
These are common timing ranges used for pregnancy planning and routine care discussions.
| Milestone | Typical gestational window | Practical note |
|---|---|---|
| Dating ultrasound | 8w0d to 13w6d | Earlier ultrasound is usually more accurate for dating than later scans |
| First-trimester screening | 11w0d to 13w6d | Timing may vary depending on local screening pathway and clinician advice |
| Anatomy ultrasound | 18w0d to 22w0d | Often used for detailed structural review in mid-pregnancy |
| Gestational diabetes screening | 24w0d to 28w0d | Common window for screening many pregnancies |
| Group B strep screening | 36w0d to 37w6d | Late-pregnancy screening window before delivery planning |
| Estimated due date | 40w0d | Actual birth may happen before or after the due date |
Frequently Asked Questions
How is pregnancy usually dated?
Traditional pregnancy dating starts from the first day of the last menstrual period and estimates a due date 280 days later. When conception date is known, the estimate is usually 266 days from conception.
Why can ultrasound change the due date?
Ultrasound can provide a different gestational age estimate than cycle dating, especially when cycles are irregular or the exact LMP is uncertain. Early ultrasound is usually more accurate for pregnancy dating than later ultrasound.
How does IVF dating work in this calculator?
The calculator uses embryo transfer date and embryo age at transfer. This allows the schedule to be anchored more precisely than a standard LMP estimate in many IVF pregnancies.
Does the baby usually arrive on the due date?
No. The due date is an estimate at 40 weeks, not a guarantee. Many births happen before or after that day.
Can I use this instead of prenatal care?
No. This tool is for education and planning only. Always follow the dates, testing schedule, and medical advice from your prenatal care team.