Estimate your baby’s due date, conception date and current pregnancy week from your last period.
Calculated privately in your browser — nothing is uploaded.
How is a pregnancy due date calculated?
Using Naegele's rule: due date = LMP + 280 days, adjusted by (cycle length − 28) days, with estimated conception ≈ LMP + 14 days. A full-term pregnancy averages 40 weeks from the last period. For an LMP of 1 January with a 28-day cycle, the due date is about 8 October. It's an estimate your provider may refine by ultrasound.
Understanding your result
A full-term pregnancy averages 40 weeks from the LMP. The result is an estimate — your provider may refine it with an ultrasound dating scan.
Formula and method
Naegele’s rule: due date = LMP + 280 days, adjusted by (cycle length − 28) days. Estimated conception ≈ LMP + 14 days (cycle-adjusted).
Assumptions and limitations
This is an estimate for general information, not medical advice, and it does not confirm or monitor a pregnancy. It assumes regular cycles and ovulation near mid-cycle, which varies between people. A clinician's dating scan is more accurate, and only your provider can assess your individual circumstances.
Worked example
For an LMP of 1 January with a 28-day cycle, the estimated due date is about 8 October and conception around 15 January.
How to use this tool
- Enter the first day of your last menstrual period (LMP).
- Set your average cycle length, or leave it at 28 days.
- Press Calculate to see your due date and current week.
Common mistakes to avoid
- Entering the conception date instead of the first day of your last period.
- Assuming the due date is exact — only about 1 in 20 babies arrive on it.
About the Pregnancy Due Date Calculator
The Pregnancy Due Date Calculator estimates your expected delivery date (EDD) using Naegele’s rule and adjusts for your cycle length, then shows how far along you are right now.
Who should use this tool
Expecting parents who want a quick estimate of their due date, conception window and current pregnancy week between appointments.
Benefits
- Estimates your due date, conception date and current pregnancy week from a single last-period entry.
- Adjusts for cycle lengths other than 28 days for a more personalised estimate.
- Works privately in your browser, with no personal dates sent anywhere.
- Explains the calculation using Naegele's rule so you can see how the date is reached.
Practical use cases
- Getting an early sense of your expected delivery date before a dating scan.
- Understanding roughly how many weeks along you are right now.
- Estimating a likely conception window from your last period.
- Planning appointments and preparation timelines around an approximate due date.
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Frequently asked questions
How accurate is the due date?
It’s a statistical estimate. A dating ultrasound in the first trimester is the most accurate way to confirm it.
My cycle isn’t 28 days — does that matter?
Yes. A longer or shorter cycle shifts ovulation, so the calculator adjusts the due date by the difference from 28 days.
Can I use this if I don't know my exact last period date?
The calculation depends on the first day of your last menstrual period, so an uncertain date makes the estimate less reliable. If you are unsure, enter your best recollection and treat the result as approximate. A clinician can provide firmer dating using an ultrasound scan.