What does a pregnancy calculator tell you?
A pregnancy calculator turns one date you know into a complete picture of your pregnancy. With a single entry, this Pregnancy Calculator shows:
- How many weeks and days pregnant you are today — the gestational age your midwife or doctor uses.
- Your estimated due date, the day the pregnancy reaches 40 weeks.
- Your trimester and approximate month of pregnancy.
- What typically happens this week, with a rough size comparison for the baby.
- Days remaining and how far through the 40 weeks you are.
- Key dates such as the end of the first trimester, the anatomy-scan window and full term.
It runs entirely in your browser, needs no sign-up and does not store what you enter.
How the pregnancy calculator works
Every pregnancy is measured on the same scale: 40 weeks (280 days) counted from the first day of the last menstrual period. Whatever you enter, the calculator converts it to that scale:
| You know… | How it is converted |
|---|---|
| The first day of your last period | Used directly; due date = + 280 days, adjusted for your cycle length |
| Your conception or ovulation date | Conception is about day 14, so due date = + 266 days |
| Your IVF transfer date | Due date = + (266 − embryo age) days, e.g. + 261 for a day-5 blastocyst |
| An ultrasound result | Due date = scan date + (280 − gestational age on the scan) |
| Your due date | Used directly; your week today = (280 − days left) ÷ 7 |
Because all methods end on the same 40-week scale, the week of pregnancy, trimester and milestones line up whichever date you start from. For the full explanation of each formula, see the Due Date Calculator.
Reading your pregnancy calculator result
- Weeks and days: “18 weeks, 3 days” means 18 full weeks have passed since the first day of your last period, and you are in your 19th week.
- Trimester and month: the trimester follows the standard split (first to 13 weeks 6 days, second to 27 weeks 6 days, third from 28 weeks); the month is an approximation, since months and weeks do not divide evenly.
- Pregnancy progress: the share of the 40 weeks that has passed. Halfway is 20 weeks.
- Days remaining: the days until the estimated due date — remember most babies arrive within about two weeks either side of it.
- Estimated conception: roughly two weeks after the start of the last period; the baby’s own age (fetal age) is counted from here, so it is about two weeks less than the pregnancy week.
- This week: a short summary of what commonly happens and a rough size comparison for the baby.
Pregnancy calculator by last period (LMP)
The LMP method is the default because almost everyone can find the date in a diary or period-tracking app. Enter the first day of real bleeding — not spotting, and not the day the period ended. If your cycles are usually longer or shorter than 28 days, open Cycle length and enter your average: a 32-day cycle moves the due date and your week number by four days, because ovulation most likely happened later. If your periods are irregular, the result is a provisional estimate until your first scan.
Pregnancy calculator by conception date
If you tracked ovulation, had IUI, or know the single date you could have conceived, choose Conception date. The calculator treats that date as two weeks of pregnancy and adds 266 days for the due date. Bear in mind that sperm can survive for several days, so conception may have happened a few days after intercourse; the Conception Date Calculator explains the fertile window.
Key dates in your result
Open Show key pregnancy dates in your result for a personal calendar: when a home test is usually positive, the end of the first trimester, the common anatomy-scan window, the start of the third trimester, early term (37 weeks), full term (39 weeks), the due date, late term (41 weeks) and post-term (42 weeks). You can print the result or share it as a link to keep the dates handy.
How many weeks pregnant am I?
Your week of pregnancy is the number of days since the first day of your last period, divided by 7. If your period started 75 days ago, you are 10 weeks and 5 days pregnant (75 = 10 × 7 + 5), which is written 10w5d and means you are in week 11. The first two of those weeks happen before conception, which is why a positive test often comes at “4 weeks” even though conception was only about two weeks earlier.
If you only know your due date — for example after a dating scan — choose Due date above. The calculator counts back 280 days and gives you the same week number your care team uses. The Pregnancy Week Calculator focuses on just this number if that is all you need.
Pregnancy calculator by due date
A pregnancy calculator based on a due date works backwards: it subtracts 280 days to find the equivalent first day of the last period and 266 days to estimate conception, then counts forward to today. This is the method to use once your provider has given you an official due date, because that date may differ from the one worked out from your period. The Reverse Due Date Calculator shows the conception window in more detail.
Your pregnancy week by week
The result tells you what typically happens in your current week. Over the whole pregnancy, the weeks fall into three trimesters:
- Weeks 1–13 (first trimester): conception, implantation and the formation of the major organs. Early symptoms are common and many people have their first appointment and dating scan.
- Weeks 14–27 (second trimester): rapid growth, the anatomy scan around 18–22 weeks, and usually the first movements.
- Weeks 28–40+ (third trimester): weight gain and maturing lungs and brain; appointments become more frequent until birth.
For every week on the calendar, open the Pregnancy Timeline, or jump to a particular week such as 8 weeks, 20 weeks or 32 weeks pregnant.
Pregnancy calculator or due date calculator?
Both use the same maths. A due date calculator answers one question — when is my baby due? — while a pregnancy calculator answers the everyday ones: how far along am I, which trimester am I in, and what is happening this week? Use whichever matches your question; the dates will always agree. If you are planning around the due date, the Due Date Calculator also lists every milestone date and offers a printable summary.
Pregnancy calculator for IVF
For IVF and frozen embryo transfers, choose IVF transfer and enter the transfer date and embryo age. The calculator converts it to gestational weeks exactly as your clinic does — on the day of a day-5 transfer you are 2 weeks 5 days pregnant. More detail, including “days past transfer” tables, is on the IVF Due Date Calculator and the FET Due Date Calculator.
Can a pregnancy calculator predict the baby’s sex?
No. A baby’s sex is set at conception and cannot be worked out from a due date, conception date or the timing of intercourse. Charts and calculators that claim to predict sex from dates or the parents’ ages — such as the so-called Chinese gender chart — are folklore and are right only about half the time, the same as guessing. The reliable options come from your care team: cell-free DNA blood screening (NIPT) can usually report the sex chromosomes from about 10 weeks, and the anatomy scan around 18–22 weeks can often show the baby’s sex.
Weight gain during pregnancy
Recommended weight gain depends on your weight before pregnancy. The widely used 2009 Institute of Medicine (now National Academy of Medicine) guidelines are:
| Pre-pregnancy BMI | Total gain, one baby | Per week, weeks 14–40 | Total gain, twins |
|---|---|---|---|
| Underweight (below 18.5) | 28–40 lb (12.5–18 kg) | 1–1.3 lb (0.44–0.58 kg) | No guideline |
| Normal weight (18.5–24.9) | 25–35 lb (11.5–16 kg) | 0.8–1 lb (0.35–0.50 kg) | 37–54 lb (17–25 kg) |
| Overweight (25.0–29.9) | 15–25 lb (7–11.5 kg) | 0.5–0.7 lb (0.23–0.33 kg) | 31–50 lb (14–23 kg) |
| Obesity (30 or higher) | 11–20 lb (5–9 kg) | 0.4–0.6 lb (0.17–0.27 kg) | 25–42 lb (11–19 kg) |
Calculate your own range — including where you should be at your current week — with the Pregnancy Weight Gain Calculator. These are general guidelines; your healthcare professional may advise a different target.
How accurate is a pregnancy calculator?
The arithmetic is exact, but the result is only as good as the starting date. A period date assumes ovulation around day 14; a conception date may be a few days off; an early ultrasound or an IVF transfer date is usually the most precise. Most babies are born within about two weeks of the due date, and only a small share — often quoted at around 4–5% — on the day itself. Use the result to plan, and rely on your care team for medical decisions.
Pregnancy calculators for pets and livestock
Expecting puppies, kittens or a calf? Animal pregnancies are much shorter or longer than human ones, so they need their own calculators: the Dog Pregnancy Calculator (about 63 days), the Cat Pregnancy Calculator (about 64 days) and the Cow Pregnancy Calculator (about 283 days).