Pregnancy Due Date Calculator
Due date from last period (LMP) or conception date.
Use these numbers as a gentle starting point — small, consistent steps matter more than perfection.
How to use Due Date Calculator
Estimate your pregnancy due date from your last menstrual period or conception date.
Open Due Date Calculator on toolpermarket, then enter the values you want to work with.
In the Based on field, pick last period (LMP) or a known conception date. LMP is the most common input.
In the Date field, enter the LMP or conception date. Use the calendar picker for an exact day.
Press Calculate to compute the result. The output appears immediately below the form. Tweak any field and run it again to check a different scenario.
Read the result and use it as needed. If the number looks off, re-check your inputs and run it again — the math is deterministic, so the same entries always return the same answer.
Worked example. An LMP of 2026-01-01 gives an estimated due date of 2026-10-08, which is 40 weeks later.
Tips for accurate results.
Due dates are estimates within about a two-week window.
Conception-based dating skips the uncertain two weeks before ovulation.
Use the LMP unless you know conception exactly.
When to use Due Date Calculator. Estimating when a baby is due. Planning appointments and leave. Converting a known conception date to a due date.
When you actually reach for this
- You are estimating a pregnancy due date from the last menstrual period.
- You want the range of likely delivery weeks, not a single day.
Where this tool stops being accurate
- It uses Naegele rule (LMP plus 280 days); only about 4 percent of babies arrive exactly on that date.
- It assumes a 28-day cycle; irregular cycles or known ovulation dates shift the real window.
Frequently asked questions
How accurate is a due date?
A due date is an estimate, not a precise deadline. Most babies arrive within about two weeks of it. It is computed as 280 days from the last period, which assumes a 28-day cycle and ovulation near day 14. You’ve got this.
LMP or conception date — which is better?
LMP is easier to recall and is the standard, but it assumes a regular cycle. If you tracked ovulation or know the conception date, that input can be more precise for you specifically. You’ve got this.
Why is it 40 weeks from the last period?
Because pregnancy is counted from the first day of the last period, which is about two weeks before conception. That convention makes the math consistent across clinics even though actual fetal age is roughly 38 weeks. You’ve got this.
Is the due date exact?
No. It is an estimate; most births fall within a two-week window around it. Use it as a midpoint, not a deadline. You’ve got this.
What if my cycle is not 28 days?
The LMP method assumes a 28-day cycle. If yours differs, an ultrasound or known ovulation date gives a better estimate. You’ve got this.