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Pregnancy Due Date Calculator

Estimate your pregnancy due date from the first day of your last menstrual period using Naegele's rule. Adjust for a non-28-day cycle to see your expected due date, current trimester, weeks pregnant, and days remaining.

days
Examples

Last period started 1 April 2026, average 28-day cycle.

Estimated due date
2027-01-06
Weeks pregnant
15 weeks
Days remaining
172 days
Trimester
Second
Approximate conception date
2026-04-15
Days pregnant
108 days

Second trimester — typically the most stable phase. The mid-pregnancy anatomy scan usually happens around weeks 18–22.

Estimate based on Naegele's rule. Due dates are estimates, not exact predictions. Confirm with your healthcare provider; this calculator is not a substitute for medical advice.

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Examples

How It Works

Formula

dueDate=LMP+280 d+(cycleLength−28) d\text{dueDate} = \text{LMP} + 280\,\text{d} + (\text{cycleLength} - 28)\,\text{d}

conceptionDate≈LMP+14 d+(cycleLength−28) d\text{conceptionDate} \approx \text{LMP} + 14\,\text{d} + (\text{cycleLength} - 28)\,\text{d}

daysPregnant=today−LMP\text{daysPregnant} = \text{today} - \text{LMP}

weeksPregnant=⌊daysPregnant7⌋\text{weeksPregnant} = \left\lfloor \frac{\text{daysPregnant}}{7} \right\rfloor

Variables

LMP\text{LMP}

First day of the last menstrual period

cycleLength\text{cycleLength}

Average length of the menstrual cycle(days)

dueDate\text{dueDate}

Estimated date of delivery

conceptionDate\text{conceptionDate}

Approximate date of conception (LMP + ~14 days, cycle-adjusted)

daysPregnant\text{daysPregnant}

Whole days elapsed since the LMP(days)

weeksPregnant\text{weeksPregnant}

Completed weeks of pregnancy(weeks)

Enter the first day of your last menstrual period (LMP). The calculator adds 280 days (40 weeks) to estimate the due date — Naegele's rule. If your cycle is shorter or longer than 28 days, the due date shifts by the same number of days, because ovulation usually happens about 14 days before the next expected period. Today's date is compared against the LMP and the due date to show your current trimester, weeks pregnant, and days remaining.

Frequently Asked Questions

01How accurate is the estimated due date?
Naegele's rule gives a rough target from the last menstrual period. The estimate can differ from the actual delivery date, especially if cycle timing is irregular or the LMP date is uncertain.
02How does the cycle-length adjustment work?
The 280-day rule assumes a 28-day cycle with ovulation around day 14. If your cycle is longer, ovulation happens later and the due date shifts later by the same number of days; a shorter cycle shifts it earlier. The calculator adds (cycle length − 28) days to the standard 280-day estimate.
03What is Naegele's rule?
Naegele's rule estimates the expected delivery date as the first day of the last menstrual period plus 280 days (40 weeks). It assumes a regular 28-day cycle and ovulation on day 14, which is why a cycle adjustment is offered for non-standard cycles.
04How are trimesters defined here?
Using the common clinical convention measured from LMP: first trimester covers weeks 1–13, second trimester covers weeks 14–27, and third trimester runs from week 28 to week 40. After week 40 the calculator reports "post-term".
05Why does it ask for the first day of the last period and not the conception date?
The exact day of conception is rarely known, but the first day of the last menstrual period is usually easy to recall and is the standard clinical anchor for pregnancy dating.

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