Enter the first day of your last period, or a due date you already have, to see how far along you are, how big your baby is this week (fruit and veggie comparisons included), and the milestones ahead.
This calculator estimates when your baby is likely to arrive based on two simple inputs: the first day of your last menstrual period (LMP) and your average cycle length. If you already have a due date from your provider or an ultrasound, you can enter it directly instead and the calculator works backwards from it. Either way, you get how many weeks and days along you are today, which trimester you're in, your estimated conception date, how big your baby is this week compared to a familiar fruit or vegetable, and a timeline of the milestones ahead.
Everything is calculated right in your browser. The dates you type in are personal, and they never leave your device or get uploaded anywhere.
The classic method is Naegele's rule: a pregnancy lasts about 280 days (40 weeks) from the first day of your last period, assuming a textbook 28-day cycle with ovulation around day 14. Because not everyone has a 28-day cycle, this tool adjusts for yours — if your cycle is longer than 28 days you likely ovulate later, so the due date shifts a little later, and vice versa:
= last period + 280 days + (cycle length − 28)If your provider has given you a due date, or you calculated it before, switch to the I know my due date option and type it in. The calculator reverses the math: it works out how many weeks and days pregnant you are today, your trimester, the estimated conception date, this week's baby size comparison, and every milestone on the timeline, all anchored to the date you were given. This is handy when an ultrasound has refined your date, since a scan-based due date is usually more accurate than one calculated from your period.
Once you enter your dates, the calculator shows the classic week-by-week comparison: your baby is about the size of a familiar fruit or vegetable, along with the average length and weight for that week. The lineup runs from a poppy seed at week 4 through a blueberry, a lemon, an avocado, a banana, an ear of corn, an eggplant, a pineapple, and on up to a watermelon at week 40. Two details worth knowing: the numbers are averages, and the measuring convention changes partway through. Up to week 20 babies are measured crown to rump (head to bottom, since their legs are curled), and from week 21 they are measured head to heel, which is why the length appears to jump between weeks 20 and 21.
| Trimester | Weeks (gestational age) |
|---|---|
| First | Weeks 1 – 13 |
| Second | Weeks 14 – 27 |
| Third | Weeks 28 – 40 |
A due date is an estimate, not a deadline. Only about 1 in 20 babies are born on their exact due date, and most arrive in the two weeks before or after. If you have irregular cycles, aren't sure of your last period, or conceived through IVF, an early ultrasound gives a more precise date — and your provider's date always takes precedence over any calculator. This tool is for general information and is not a substitute for medical care.
Enter the first day of your last period and your average cycle length: the estimated due date is about 40 weeks from that date, adjusted for your cycle. The calculator also shows how far along you are today and the likely conception date.
Pregnancy is counted from the last period, not conception, so the calculator turns your dates into the current week and day, plus your trimester, the way your doctor will count it.
It is a well-founded estimate (the standard Naegele's rule, cycle-adjusted), but only about 1 in 20 babies arrives on the exact date. An early ultrasound refines it; think of the date as the center of a window.
The calculator shows your current week's size comparison to a familiar fruit or vegetable, from a poppy seed at week 4 to a watermelon at week 40, along with the average length and weight for that week. Sizes are averages; length is measured crown to rump through week 20 and head to heel after that.
Yes. Switch to the I know my due date option and enter the date from your provider or ultrasound. The calculator works backwards from it to show how many weeks pregnant you are, your trimester, this week's baby size comparison, and the milestone timeline.
Completely, and here that genuinely matters: the calculation runs on your device, and no advertising system learns you asked. Nobody should find out from a coupon mailer.