Pregnancy Calculator Online
Track how many weeks pregnant you are, your trimester, and due date from your last period or a known due date, right in your browser.
Your dates are calculated locally in your browser and never leave your device. This tool gives a general estimate from a standard formula and is not medical advice.
Open the Due Date Calculator
About Pregnancy Calculator
Pregnancy Calculator estimates how far along a pregnancy is — in weeks and days, trimester, and an estimated due date — from either the first day of the last menstrual period or a known due date. Pick the date you know, choose an "as of" date (today by default), and the tool instantly shows completed weeks and days, which trimester you are in, the due date using the standard 280-day (40-week) estimate, and a simple trimester timeline. It is useful for expecting parents tracking milestones, partners planning ahead, or anyone estimating a due date before a first prenatal visit. This is a general estimate from a standard formula, not medical advice — every pregnancy is different, so confirm dates with a doctor or midwife. Everything runs locally in your browser; nothing is uploaded.
Features
- Calculates gestational age in completed weeks and days from the last menstrual period
- Works the other direction too — enter a known due date to back-calculate the likely last period
- Shows which trimester you are in, with the exact date range for all three
- Estimates the due date using the standard 280-day (40-week) rule
- Displays a progress bar showing what percent of the pregnancy is complete
- Lets you calculate progress as of any date, not just today
- Copies a plain-text summary of weeks, trimester, and due date
- Runs entirely in your browser — your dates are never uploaded
How to use the Pregnancy Calculator
- Choose whether you know your last period date or your due date
- Enter that date, and optionally change the "calculate as of" date from today
- Read off the weeks and days along, trimester, and estimated due date
- Copy the summary or check the trimester timeline for the date ranges
Example
Input
LMP 12 weeks ago
Output
12 weeks (2nd trimester)
A last period that began 12 weeks ago puts you 12 weeks along, in the second trimester.
Common errors & troubleshooting
- Entered a due date but left the mode on "Last period". — Switch to the "Due date" toggle first so the calculator back-calculates the last period correctly.
- The result shows 0 weeks 0 days unexpectedly. — This means the "calculate as of" date is before the last-period date — pick an as-of date on or after it.
- Progress bar shows past 100%. — That is expected once the "calculate as of" date is after the estimated due date — pregnancies often run past the due date.
- Confusing the last menstrual period (LMP) with the conception date. — LMP is the first day of the last period, roughly two weeks before ovulation — enter LMP, not the conception date, unless you use the "Due date" mode.
Frequently asked questions
- What does the Pregnancy Calculator use to estimate my due date?
- It adds 280 days (40 weeks) to the first day of your last menstrual period, the same standard formula used for an initial estimate. If you already know your due date, switch modes to back-calculate the last period instead.
- How accurate is the Pregnancy Calculator's due date?
- It gives a general estimate based on a standard 280-day cycle, not an ultrasound-confirmed date. Actual due dates vary, so treat the result as a planning estimate and not medical advice.
- Can I use the Pregnancy Calculator with a due date instead of my last period?
- Yes. Switch the toggle to "Due date", enter the date your provider gave you, and the calculator back-calculates the equivalent last-period date to compute weeks and trimester.
- How does the Pregnancy Calculator decide which trimester I'm in?
- It classifies the pregnancy by completed gestational week: earlier weeks are the first trimester, the middle stretch is the second, and the final weeks are the third, matching the trimester ranges shown in the timeline.
- Does the Pregnancy Calculator send my dates anywhere?
- No. All the math happens locally in your browser. The dates you enter are not uploaded or stored by ArrayKit.
- Can I check pregnancy progress for a date other than today?
- Yes. Change the "calculate as of" date to any day — past or future — to see weeks, trimester, and progress as of that date.
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