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Pregnancy & Maternal Health ACOG/obstetric dating convention Activated — LMP-based educational estimate Higher-risk clinical context

Pregnancy Due Date Calculator from LMP

Estimate due date and current gestational age from the first day of the last menstrual period, with cycle-length adjustment.

Use calculator View formula

Interactive tool

Calculator

Enter values carefully. Results appear after calculation and should be interpreted with the safety notes and source method on this page.

Activated — LMP-based educational estimate

Step 1 — Enter inputs

3 fields required for this tool

Step 2 — Review the result

The result area updates below and keeps safety wording visible.

Result

Complete the form and select Calculate.

About this calculator

This LMP due date calculator estimates your due date from the first day of your last menstrual period. It also estimates how many weeks pregnant you are today.

LMP dating assumes reasonably regular cycles and ovulation timing. Ultrasound or IVF dating may be more appropriate in many pregnancies.

Source-backed
Uses the conventional 280-day pregnancy dating method from the first day of the last menstrual period, with optional cycle-length adjustment. Accurate clinical dating may require ultrasound confirmation.
Review status
Activated — LMP-based educational estimate
Limitations
LMP-based due dates can be inaccurate with irregular cycles, uncertain dates, recent hormonal contraception, breastfeeding, or assisted reproduction.

Formula and method

EDD = first day of LMP + 280 days + (cycle length − 28 days). The cycle adjustment is an estimate and should not override clinician-recorded dating.

Medical safety note: This page is for education only and should not replace professional medical advice. For emergencies, medication decisions, or severe symptoms, contact a qualified clinician or local emergency service.

Limitations and when not to rely on this result

  • LMP-based due dates can be inaccurate with irregular cycles, uncertain dates, recent hormonal contraception, breastfeeding, or assisted reproduction.
  • Ultrasound dating and clinician guidance may supersede LMP estimates.
  • Do not use this page for urgent pregnancy symptoms or decisions about induction, viability, or fetal growth.

Frequently asked questions

How is a due date calculated from LMP? +

A common obstetric convention estimates the due date as 280 days, or 40 weeks, from the first day of the last menstrual period.

Why does cycle length matter? +

Longer or shorter cycles may shift ovulation timing, so the calculator optionally adjusts the estimate relative to a 28-day cycle.

What if my periods are irregular? +

LMP dating may be less accurate. Ask your clinician whether ultrasound or another dating method should be used.

Is the due date exact? +

No. A due date is an estimate used for pregnancy care planning; most births do not happen exactly on the due date.

Can I use this for IVF pregnancy? +

IVF dating usually uses embryo transfer or fertilization timing. Use your fertility clinic’s documented EDD rather than this LMP estimate.