Category
Parenting & Family
Baby Due Date Calculator
Estimate due date using LMP or current gestational age, with a simple timeline view
Estimated time
1 min
Baby Due Date Inputs
Use either last period details or current gestational age to estimate due date and timeline milestones.
Estimate mode
Use the first day of your last menstrual period. This anchors the LMP-based due date estimate.
If your cycle is not 28 days, this adjusts ovulation timing and shifts the estimate slightly.
days
Use the week count provided by your care team or ultrasound report.
weeks
days
Use the date when this gestational age was recorded. The estimate projects forward from that date.
Formula Summary
LMP due date = LMP date + 280 days + (cycle length - 28)
Conception estimate = LMP date + (cycle length - 14)
Gestational mode due date = reference date + (280 - gestational days)
Gestational age (weeks) = floor(total gestational days / 7)
Weeks until due = remaining days / 7
How It Works
This calculator offers two common planning paths: LMP-based estimation and gestational-age-based estimation.
It is designed for planning and conversations, not diagnosis. Your care team can provide the most accurate dating.
- LMP mode starts from the first day of your last period and applies the 280-day pregnancy estimate.
- Cycle length can shift ovulation timing and move the estimated due date by a few days.
- Gestational mode starts from your current week/day count and projects forward to 40 weeks total.
- Trimester labels are estimated from gestational week ranges: first (0-13), second (14-27), third (28+).
- Most babies arrive within a window around the estimated date, not exactly on one day.
Example Calculations
LMP estimate
LMP on 2026-01-08, 28-day cycle
Estimated due date in mid-October 2026
Standard cycles usually align closely with the 280-day estimate.
Gestational-age estimate
Reference date today, 20 weeks 3 days
About 19.5 weeks remaining
Gestational mode is useful when your care team has already shared a week/day estimate.
Longer cycle estimate
LMP on 2026-01-08, 32-day cycle
Due date shifted a few days later
Longer cycle assumptions move ovulation and due date estimates later.
Frequently Asked Questions
How accurate is an estimated due date?
It is a planning estimate. Many births occur before or after the estimated date, so treat it as a range marker.
Should I use LMP mode or gestational mode?
Use LMP mode when your last period date is reliable. Use gestational mode when a week/day estimate is already known.
Can this replace prenatal care?
No. This tool is informational only and should not replace medical advice, diagnosis, or prenatal monitoring.
Why does cycle length matter?
Cycle length can shift ovulation timing, which can slightly move both conception and due date estimates.
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