Pregnancy Calculator
Estimate gestational age, trimester and due date from your last period date.
Enter your last period date to estimate your gestational age and due date.
Pregnancy Calculator on True Calculator gives you an instant, accurate answer with no sign-up and no app install. Estimate gestational age, trimester and due date from your last period date. Every result shows the formula and a worked example so you can verify the calculation yourself, and all values are computed in your own browser — your numbers never leave your device.
Popular uses: pregnancy calculator · gestational age calculator · pregnancy week calculator
How We Calculate
This calculator uses medically reviewed formulas verified by our team. All calculations are performed instantly in your browser using JavaScript — no data is sent to any server.
We use WHO-recommended formulas and medical standards for health calculations. Results are estimates, not medical advice — always consult a doctor for health decisions.
When to Use This Calculator
Use the pregnancy calculator whenever you want a quick, privacy-friendly way to know where you stand in pregnancy — checking your week, your trimester, or how far along you are before your next doctor's visit. It is handy for planning maternity leave, estimating when antenatal check-ups and scans should happen, and preparing the family calendar around an expected delivery window. Because it only needs your LMP, it works even before a first scan appointment, and you can re-check it any week without remembering your weight or other details. It is also useful for partners and family members who want to follow the pregnancy milestones week by week. The tool is educational only: it does not diagnose, confirm pregnancy or replace antenatal care, so always share your dates with your doctor.
How to Use This Calculator
- Step 1: Select the first day of your last menstrual period (LMP) in the date field.
- Step 2: Review the gestational age shown in weeks and days, counted from that LMP.
- Step 3: Read your estimated due date, which is 280 days from the LMP.
- Step 4: Note the trimester and weeks remaining, then confirm everything at your next antenatal visit.
Worked Example
An expectant mother in Bengaluru enters 10 January 2026 as her LMP. On 14 August 2026 the calculator shows she is 30 weeks and 6 days pregnant, with 216 days of pregnancy completed. Her estimated due date works out to 17 October 2026, conception is placed around 24 January, and about 10 weeks remain until the due date. Her pregnancy falls in the third trimester. These figures come straight from the 280-day rule, so they are estimates — her doctor will adjust them if an early scan suggests a different date.
Tips and Common Mistakes
- •Tip 1: Note your LMP in a calendar app as soon as your period starts, since every date in pregnancy builds on it.
- •Tip 2: If your cycle is longer than 28 days, expect ovulation (and the due date) to shift later by roughly the difference.
- •Tip 3: Use the same LMP across tools and apps so your doctor sees one consistent gestational age.
- ✗Mistake 1: Entering the date your period ended instead of the first day it began, which shifts every result by several days.
- ✗Mistake 2: Treating the due date as an exact birth date — a range of 37 to 42 weeks is considered normal.
Frequently Asked Questions
How does the pregnancy calculator estimate my due date?
It adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This is the standard Naegele's rule that assumes a 28-day cycle with ovulation around day 14.
Why does gestational age start from my period, not conception?
Doctors date pregnancy from the LMP because the period date is usually known, while ovulation is not. Conception happens roughly two weeks after the LMP, so a '10-week pregnancy' means the baby is about 8 weeks from conception.
What if my cycle is longer than 28 days?
The 280-day estimate assumes a 28-day cycle. With a longer cycle, ovulation and conception shift later, so your due date may be a few days later. An early ultrasound remains the most reliable way to date the pregnancy.
How accurate is the due date?
Only about 4% of babies arrive exactly on the due date. Most are born between two weeks before and two weeks after it, so treat the date as a guide rather than a guarantee.
Is this calculator a substitute for a doctor's visit?
No. These are general estimates and are not a diagnosis. Always confirm your dates and care plan with a doctor, especially if your periods are irregular or you are unsure of your LMP.
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