Pregnancy CalculatorFree online fitness & health calculator — instant results, no sign-up
Pregnancy schedule from last period, due date or conception.
For general information only. This is not medical advice, diagnosis, dosing guidance or a treatment recommendation. Talk to a doctor or other qualified health professional about your health, pregnancy, or diet.
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About the Pregnancy Calculator
The Pregnancy Calculator estimates key milestones across a pregnancy schedule based on your last menstrual period, an established due date, or estimated conception date. It tracks your current gestational age in completed weeks and days, identifies your current trimester, and projects trimester completion dates. Expectant parents and healthcare planners use this schedule to track gestational development.
- Calculate based on
- The reference event used to anchor the schedule: Last period (first day of LMP), Due date (estimated delivery date), or Conception date.
- Date
- The calendar date corresponding to the chosen reference event.
Formula and method
LMP = D (if Last period) | Due date − 280 days | Conception date − 14 days Due Date = LMP + 280 days Gestational Days = Today − LMP Weeks Pregnant = floor(Gestational Days / 7) weeks and (Gestational Days mod 7) days End of 1st Trimester = LMP + 91 days (13 weeks) End of 2nd Trimester = LMP + 189 days (27 weeks) Estimated Conception = LMP + 14 days
- LMPCalculated or entered first day of the last menstrual period
- DUser-selected input date
- Gestational DaysElapsed calendar days from the LMP date to the current date
The tool first normalizes the input date to an equivalent LMP date by subtracting 280 days from an estimated due date or 14 days from a conception date. It calculates the estimated due date at exactly 280 days (40 weeks) from the LMP and determines current gestational age by taking elapsed days to the present date. Trimesters are assigned based on completed weeks: First trimester is under 13 weeks, Second is weeks 13 through 26, and Third begins at 27 weeks.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Calculate based onLast period
- Date1969-11-02
Results
- Due dateSun, August 9, 1970
- Weeks pregnant today2974 weeks 1 days
- TrimesterThird
- End of 1st trimesterSun, February 1, 1970
- End of 2nd trimesterSun, May 10, 1970
- Conception (est.)Sun, November 16, 1969
How to use the Pregnancy Calculator
- 1Select your reference starting point: Last period, Due date, or Conception date.
- 2Enter the specific calendar date corresponding to that reference point.
- 3Convert the entered date to an equivalent LMP baseline (LMP = Due date − 280, or LMP = Conception − 14).
- 4Read your estimated due date, current gestational age in weeks and days, trimester boundaries, and estimated conception date.
Reading your result
Your estimated due date marks the standard 40-week gestation mark. The gestational age shows how many full weeks and additional days have elapsed since the start of your menstrual cycle baseline, not since the day of fertilization. Trimester dates indicate the exact day the first trimester ends (13 completed weeks) and the second trimester ends (27 completed weeks).
Limitations
The calculation assumes a regular 28-day menstrual cycle with ovulation and fertilization occurring precisely on cycle day 14. It does not account for irregular cycles, luteal phase variations, IVF transfer timing, or clinical dating adjustments from first-trimester ultrasound measurements.
Common questions
Why does gestational age include two weeks before conception occurred?+
Obstetric convention measures gestational age from the first day of the last menstrual period (LMP) rather than fertilization, because menstrual bleeding is a clearer historical event than exact ovulation. As a result, standard pregnancy dating includes roughly two weeks prior to conception.
How are the trimester boundaries defined in this calculator?+
The calculator marks the end of the first trimester at 91 days (exactly 13 weeks) from the LMP date, and the end of the second trimester at 189 days (exactly 27 weeks). Gestational ages under 13 completed weeks are classified as First trimester, 13 to 26 weeks as Second, and 27 weeks or more as Third.
What happens if the calculated gestational days result in a negative number?+
If the selected LMP date or derived LMP falls in the future relative to today's date, gestational progress will display as 'Not yet', while milestone dates like the estimated due date will still project forward normally.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
You might also like
Pregnancy Weight Gain Calculator
Recommended weight gain by pre-pregnancy BMI.
Pregnancy Conception Calculator
Likely conception window from due date.
Due Date Calculator
Estimated due date from your last period and cycle length.
Ovulation Calculator
Fertile window and ovulation day for upcoming cycles.
Conception Calculator
Estimate when conception likely happened from due date.
Period Calculator
Predict your next periods.
Results are estimates for informational purposes and are not financial, medical or legal advice.