LMP to Due Date Calculator

Plan pregnancy timelines from your cycle details confidently. Review milestones, reminders, and due date adjustments. Save results for visits, checklists, records, and shared planning.

White theme Cycle-adjusted estimate CSV export PDF export

Enter pregnancy dating details

Use the first day of the last menstrual period and optional cycle settings for a more tailored estimate.

First day of last menstrual period

Reference date

Average cycle length (days)

Luteal phase length (days)

Gestation after ovulation (days)

Baby label or nickname

Notes

Formula used

Standard rule: Estimated due date = LMP + 280 days.

Cycle-adjusted rule: Ovulation date = LMP + (cycle length − luteal phase).

Advanced due date formula: Due date = Ovulation date + gestation after ovulation.

Pregnancy age: Gestational age = reference date − LMP, shown as weeks and days.

Default settings reproduce the classic 280-day estimate when cycle length is 28 days, luteal phase is 14 days, and gestation after ovulation is 266 days.

How to use this calculator

Enter the first day of the last menstrual period.
Choose a reference date to see pregnancy age on that day.
Keep the default cycle values or adjust them to match your typical cycle.
Optionally add a baby label and notes for exported records.
Press Calculate timeline to show results above the form.
Review due date, trimester starts, scan windows, and days remaining.
Use the CSV or PDF buttons to save a shareable copy.

Example data table

LMP date	Cycle length	Luteal phase	Ovulation estimate	Due date estimate	Reference date	Pregnancy age
Jan 10, 2026	28 days	14 days	Jan 24, 2026	Oct 17, 2026	Mar 7, 2026	8 weeks 0 days
Dec 15, 2025	30 days	14 days	Dec 31, 2025	Sep 23, 2026	Mar 7, 2026	11 weeks 5 days
Nov 20, 2025	26 days	13 days	Dec 3, 2025	Aug 26, 2026	Mar 7, 2026	15 weeks 2 days

Why these outputs help

Planning milestones

Trimester start dates and scan windows help organize checkups, preparation tasks, and personal planning in one place.

Cycle-based adjustment

Custom cycle and luteal values can improve the estimate when cycles differ from the 28-day assumption.

FAQs

1. What does LMP mean?

LMP means last menstrual period. This calculator uses the first day of that period as the starting point for estimating gestational age and a projected due date.

2. Why is the default due date based on 280 days?

A common pregnancy estimate is 280 days from the LMP. That standard assumes ovulation about 14 days into a 28-day cycle.

3. Should I change the cycle length field?

Yes, if your usual cycle is clearly shorter or longer than 28 days. A custom cycle length can shift the estimated ovulation and due date.

4. What is the luteal phase field for?

The luteal phase is the time between ovulation and the next period. Adjusting it changes the estimated ovulation day inside your cycle.

5. Is this calculator a medical diagnosis tool?

No. It provides an estimate for planning and recordkeeping. Clinical dating may use ultrasound findings and professional judgment.

6. Why might my clinician give a different due date?

Ultrasound measurements, uncertain LMP dates, irregular cycles, or specific medical considerations can lead to a different estimated due date.

7. Can I export the results?

Yes. After calculating, use the CSV or PDF buttons above the form. They save a convenient copy of the displayed timeline.

8. What if the reference date is before the LMP?

The calculator still shows timeline dates, but pregnancy age will not be counted yet. Check the dates and recalculate if needed.

Important: This tool is for educational and planning use. Pregnancy dating and prenatal decisions should always be confirmed by a qualified healthcare professional.