LMP-based dating counts from before conception
That is why gestational age is typically about two weeks ahead of embryonic age in standard obstetric dating.
Clinical dating
Pregnancy Due Date Calculator
Calculator
Results
Ready to calculate
Use the controls on the left and calculate to see your result, units, and interpretation.
Use the controls on the left and calculate to see your result, units, and interpretation.
About This Tool
A due date estimate is one of the most common date calculations people look up during pregnancy planning. Even when a clinic provides an official date later, many people want an early private estimate for appointments, leave planning, travel decisions, or milestone tracking. This Pregnancy Due Date Calculator supports the common starting points: the first day of the last menstrual period, a conception date, or an IVF transfer date. It then translates that information into an estimated due date and a few practical milestone dates.
The calculator is designed to be simple but explicit about its assumptions. In last-menstrual-period mode, it uses the standard obstetric framework of 280 days and adjusts that estimate by cycle length when you provide a value other than 28 days. In conception mode, it counts forward 266 days, which reflects the more direct developmental timing from conception. In IVF mode, the embryo transfer date plus embryo age provides the estimate. These are standard planning conventions, but they are still estimates rather than guarantees.
The result includes the due date, the approximate gestational age on a chosen reference date, and the approximate start of the second and third trimesters. That gives the page practical value beyond a single date. It helps with scheduling, household planning, travel windows, and conversations with employers or family. Because the entire calculation runs in the browser, it is also suitable for private use when you are not ready to store anything in another service.
It is important to treat the output as informational. Clinical dating may change after an ultrasound or based on individualized medical advice. This page is therefore best used as a planning and understanding tool rather than as a substitute for professional care. Within that boundary, it provides clear date math and milestone context in a compact, privacy-first format.
Formula
LMP due date = LMP date + 280 days + (cycle length − 28)conception due date = conception date + 266 daysIVF due date = transfer date + (266 − embryo age in days)
Example Calculation
Example: if the last menstrual period began on 2026-01-01 and the cycle length is 28 days, the standard estimate adds 280 days to produce a due date in early October 2026. The page then calculates the gestational age and trimester milestone dates from that estimate.
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FAQs
Which methods can I use?
You can estimate from the last menstrual period, conception date, or IVF transfer date.
Why does cycle length matter in LMP mode?
If ovulation happens earlier or later than day 14 in a 28-day cycle, the estimated due date may shift slightly when adjusting from the LMP method.
Does this replace prenatal medical care?
No. It is an informational planning calculator and not a substitute for ultrasound dating or clinical assessment.
What milestones are shown?
The result includes estimated due date, approximate gestational age at the reference date, and the start of the second and third trimesters.
Is any health data uploaded?
No. Dates stay in your browser and are not sent to a server.
5 Facts
Cycle length can move the estimate
A longer or shorter ovulation pattern can shift the expected due date slightly when using LMP.
Timing
Only a minority of births happen exactly on the due date
The due date is a planning estimate, not a precise delivery prediction.
Expectations
Trimester dates are useful for planning
Appointments, leave planning, and personal milestones are often organized around trimester boundaries.
Preparation
IVF dating can be more exact from transfer details
Transfer timing provides a more specific developmental reference than a generic cycle assumption.
Fertility care
Important Note
This calculator is not medical advice and cannot replace ultrasound dating, prenatal assessment, or clinician guidance. For any pregnancy-related decision, use healthcare advice and official medical records as the authoritative source.