Pregnancy Calculator
Enter the first day of your last menstrual period to estimate your due date and track how far along you are.
Example
If your last menstrual period began on March 1, 2026, and today is May 10, 2026:
Due date = Mar 1 + 280 days = Dec 6, 2026
Days along = 70 days -> 10 weeks 0 days
Trimester = First trimester (week 10)
Remaining = 280 - 70 = 210 days
Progress = 70 / 280 = 25%
How it works
Due date is calculated as LMP + 280 days (Naegele's rule). Gestational age is the days elapsed since LMP, shown as completed weeks and days, with trimester and days remaining derived from there.
Good to know
This Pregnancy Calculator turns a single date — the first day of your last menstrual period (LMP) — into a snapshot of where a pregnancy stands. After you enter the LMP, it returns an estimated due date, your gestational age in completed weeks and days, the total days elapsed, days remaining, the current trimester, and a percent-complete progress figure. It is built for anyone who wants a quick gestational-age estimate between appointments: expectant parents, partners, and anyone trying to make sense of the "weeks pregnant" numbers used by clinicians.
You would typically use it after a missed period or a positive test, once you know roughly when your last period started. Because it also includes an "As of date" field, you can check how far along you are on any chosen day — useful for confirming a number from a past appointment or projecting where you'll be by a future date.
To read the result correctly, remember that the week count is dated from your LMP, not from conception, so it runs roughly two weeks ahead of the time since you actually conceived. Gestational age shows as completed weeks plus extra days (for example, "10w 0d" means exactly ten weeks), and trimesters here are grouped as weeks 1–12, 13–27, and 28 onward. The due date is simply LMP plus 280 days. If the elapsed time passes 294 days the badge reads "Past due," and days remaining can show as "overdue."
One practical caveat: the math assumes a regular 28-day cycle with ovulation around day 14, so if your cycles are longer, shorter, or irregular, the estimate may be off by several days. An early ultrasound is generally considered more accurate, and a provider may re-date the pregnancy based on it. Treat the output as an educational estimate rather than a confirmed timeline.
Frequently asked questions
How is the due date calculated?
It uses Naegele's rule: 280 days (40 weeks) are added to the first day of your last menstrual period. This assumes a regular 28-day cycle with ovulation around day 14.
Why does it say week 10 when conception was only about 8 weeks ago?
Pregnancy is dated from the first day of your last menstrual period, not from conception. Since ovulation happens roughly 2 weeks after LMP, gestational age is about 2 weeks more than the time since conception.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
How accurate is an LMP-based due date?
An LMP-based estimate using Naegele's rule is a reasonable starting point, but only about 4-5% of births occur exactly on the predicted date, and most fall within roughly two weeks on either side. Accuracy decreases if cycles are irregular or ovulation did not occur around day 14, which is why early ultrasound dating is often considered more reliable.
What if I don't know the first day of my last period?
If the LMP is unknown, a due date can still be estimated from an early ultrasound measurement or from a known conception or transfer date, but this calculator specifically requires an LMP date to run. A healthcare provider can establish dating when the LMP is uncertain.
How many weeks pregnant am I if my last period was 10 weeks ago?
Counting from the first day of the last menstrual period, you would be about 10 weeks of gestational age. Because pregnancy is dated from the LMP rather than conception, this is roughly two weeks more than the actual time since conception.
When does each trimester start and end?
This tool groups the first trimester as weeks 1 through 12, the second as weeks 13 through 27, and the third from week 28 onward. Different sources draw the boundaries slightly differently, so exact cutoffs can vary by a week or two.
Can the due date change during pregnancy?
Yes. A provider may adjust the due date, most often after an early ultrasound, if the measured size differs from what the LMP suggests. Once an estimated due date is established, it is usually not changed again later in pregnancy.
Does a longer or shorter cycle affect my due date?
It can. Naegele's rule assumes a 28-day cycle with ovulation near day 14, so a consistently longer cycle tends to push the actual due date later and a shorter cycle earlier than the LMP-based estimate. The calculator does not adjust for cycle length.
Is the calculator free and does it store my dates?
The tool is free to use and runs entirely in your browser. The dates you enter are processed locally and are not uploaded or stored on a server.
Related calculators