Dating Pregnancy Calculator

Usually today. Leave blank only if the caller injects a date.
5 for a blastocyst, 3 for a cleavage-stage embryo, 0 to date from egg retrieval.
How far along
21w 4d
Gestational Age Calculator
Clinical notation
21 4/7 weeks
Completed weeks
21
Extra days
4
Gestational age in days
151
Trimester
2
Trimester range
Second trimester (14 0/7 to 27 6/7 weeks)
Fetal (conceptional) age
19w 4d
Fetal age in days
137
Completed 4-week months
5
Estimated due date
2026-10-08
Due date falls on
Thursday
Dating LMP
2026-01-01
Estimated conception date
2026-01-15
Days until the due date
129
Weeks until the due date
18.43
Pregnancy complete
53.93 %
Term classification
preterm (before 37 0/7 weeks)
Dating method used
Last menstrual period, 28-day cycle
Worked out from ACOG Committee Opinion No. 700: Methods for Estimating the Due Date and 2 other sources.
Beyond the first trimester, menstrual dating is less reliable than the dating a clinician has already assigned. Use the due date on your notes if you have one.
An estimate from calendar arithmetic, not a clinical assessment. Only about 4% of births occur on the estimated due date; ultrasound dating by a clinician supersedes menstrual dating when they disagree.

How this is worked out

7 steps
  1. Ovulation is one luteal phase before the next period would start: 28 - 14 = day 14 of the cycle, so 2026-01-15.
  2. Estimated due date = ovulation + 266 days.
  3. With a 28-day cycle this is exactly Naegele's rule: LMP + 280 days.
  4. Gestational age on 2026-06-01 = 2026-06-01 - 2026-01-01 = 151 days.
  5. 151 days = 21 completed weeks and 4 day(s), written 21 4/7 weeks.
  6. Fetal (conceptional) age is 14 days less: 137 days.
  7. Days to the due date = 280 - 151 = 129.
Next milestonetable
labelgestationalAgedate
Limit of periviability24 0/7 weeks2026-06-18

Results are general information, not financial, tax, legal, medical or engineering advice.