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Find how many weeks pregnant you are from the first day of your last period (LMP) to any reference date. See completed weeks and days, trimester, estimated due date (EDD) via LMP + 280 days (40-week Naegele rule), and days before or after due date. Educational only— ultrasound dating often changes the official EDD. More tools on our medical calculators hub.
Last updated: June 4, 2026
Use today’s date for current gestational age, or an ultrasound / visit date for dating at that time.
Gestational age
27 weeks 5 days
194 completed days since LMP (27 w + 5 d)
Estimated due date (EDD)
2026-07-08
LMP + 40 weeks (280 days), Naegele-style
Versus EDD
86 days before EDD
Trimester 2
Second trimester (14 weeks 0 days through 27 weeks 6 days)
LMP dating vs ultrasound
Many pregnancies are dated by first-trimester ultrasound when LMP is unknown or inconsistent. This tool uses LMP only; use documented clinical EDD when it differs.
Demo default dates
27 weeks 5 days
Trimester 2 · EDD 2026-07-08
~12 weeks since LMP
12 weeks
Trimester 1
28 completed weeks
28 weeks
Trimester 3
Reference = LMP + 280 days
40 weeks
Due date
| Trimester | Completed weeks | Days since LMP (approx.) | Notes |
|---|---|---|---|
| First | 0 weeks 0 days through 13 weeks 6 days | 0–97 days since LMP (approx.) | Organogenesis; early screening discussions |
| Second | 14 weeks 0 days through 27 weeks 6 days | 98–195 days since LMP (approx.) | Anatomy scan era; fetal movement often perceived |
| Third | 28 weeks 0 days onward | 196+ days since LMP (approx.) | Viability discussions, growth surveillance, delivery planning |
Gestational days = calendar days from LMP to reference date
Completed weeks = floor(gestational days ÷ 7)
Extra days = gestational days mod 7
EDD = LMP + 280 days (40 weeks)
Naegele mnemonic: LMP + 1 year − 3 months + 7 days (calendar-adjusted) ≈ LMP + 280 days.
| Method | Basis | EDD approach | When used |
|---|---|---|---|
| LMP (this calculator default) | First day of last menstrual period | LMP + 280 calendar days (Naegele) | Regular cycles, reliable LMP recall |
| First-trimester ultrasound (CRL) | Crown–rump length measurement | Assigned by biometry tables | Often supersedes LMP if discrepancy beyond guideline thresholds |
| IVF / embryo transfer | Transfer date + embryo age offset | Clinic-specific (not LMP + 280) | Use IVF due date calculator—not this LMP form |
| Second-trimester ultrasound | BPD, HC, AC, FL biometry | Less preferred for initial dating if first-trimester scan done | When first-trimester dating unavailable |
Reproduces pregnancy-wheel math: calendar days since first day of LMP split into weeks and days.
Shows LMP-based due date and whether the reference date is before, on, or after that EDD.
Maps completed weeks to trimester bands used in most US prenatal education materials.
Always schedule care to your clinician’s EDD when it differs from pure LMP math.
Full term is often discussed as 37–40+ weeks for delivery timing. Only a minority deliver on the exact LMP-based EDD; many deliver in the two weeks before or after.
Related: reverse due date calculator, IVF due date calculator, adjusted age (premature infants).
Urgent pregnancy concerns (severe abdominal pain, heavy bleeding, severe headache, vision changes, reduced fetal movement) need maternity or emergency care—not this date calculator.
For expectant parents, nursing students, and childbirth educators
Suggested hashtags: #Obstetrics #Pregnancy #Prenatal #Education #Calculator