This pregnancy due date calculator estimates an educational due date from the first day of your last menstrual period (LMP) using standard dating math. It is not a diagnosis, ultrasound substitute, or care plan. Confirm dates with a qualified clinician.
Most LMP calculators assume a typical 28-day cycle and add about 280 days (40 weeks) from LMP. Irregular cycles, uncertain LMP, fertility treatment, and early ultrasound measurements can change the clinical estimated due date (EDD).
Who this due date calculator helps
People who want a quick planning estimate after an LMP date, partners preparing a calendar, and students learning how Naegele-style dating works. It is not for emergency triage or medication timing.
How to use the pregnancy due date calculator
- Enter the first day of the last menstrual period.
- Confirm the date format matches the fields shown.
- Read the estimated due date and week context the tool returns.
- If your clinician already assigned an EDD, prefer that date for appointments.
What LMP dating assumes
Classic dating assumes ovulation near the middle of a 28-day cycle. Longer cycles often mean ovulation later; shorter cycles earlier. If your cycles vary widely, the home estimate is only a starting sketch until clinical dating is available.
How the calculation works
A common educational approach adds 280 days to LMP (sometimes taught as “add one year, subtract three months, add seven days” for a 28-day cycle). Multicalify’s on-page tool follows the site’s live calculator logic—use the widget result as the source of truth for this page’s arithmetic.
Worked LMP dating example
If LMP was March 1 on a typical 28-day cycle, adding about 280 days lands near December 6. That single date is still an estimate: most births occur in a window around the EDD, not on one guaranteed day.
If LMP is uncertain by a week, the educational due date shifts with it. Re-enter the date your clinician uses rather than averaging multiple guesses.
Due date versus conception estimates
Due date math and conception-window math answer different questions. Conception usually occurs days before the midpoint assumptions baked into LMP dating. For fertile-window education, use the conception calculator, then keep prenatal scheduling aligned with clinical EDD guidance.
When ultrasound revises the date
Early ultrasound biometry can be more accurate than LMP when cycles are irregular or the LMP date is uncertain. Providers may revise the EDD when the difference exceeds their clinical threshold. Follow the revised clinical date for care decisions.
Due date mistakes with irregular cycles
- Treating a calculator date as exact labor timing
- Ignoring spotting that was not a true period
- Mixing cycle lengths without telling your clinician
- Using a conception guess as if it were an LMP
Limitations and care guidance
This page is educational only. It does not provide medical advice, diagnose pregnancy, or replace prenatal care. Contact a clinician or emergency services for urgent symptoms. Professional organizations publish clinical dating guidance for providers; your care team applies those standards to your situation.
FAQ
Is a due date exact?
No. It is an estimate. Delivery often occurs in a window around the date.
What if my cycle is longer than 28 days?
Simple LMP tools assume a standard cycle. Longer or irregular cycles may need clinical adjustment.
Can I use this after IVF?
Assisted reproduction dating often uses transfer or retrieval dates. Ask your clinic which date to use; do not force a generic LMP model.
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