How Far Along Am I? Pregnancy Weeks Calculator
Enter your due date and instantly see how many weeks and days you are on today, which trimester you are in, and how long until your baby is due.
Quick samples
Enter your due date to see how far along you are.
Add your due date (or try a quick sample) and your current week, trimester and days remaining appear here.
Weeks are counted from the implied last menstrual period — 280 days before your due date — the same reference your midwife or doctor uses.
The formula
Gestational age = (check date − (due date − 280 days)) ÷ 7 · Days to go = due date − check date
- 280 days — Forty weeks, the standard length of pregnancy counted from the last period.
- Implied LMP — The last-period start date your due date points back to; day zero of the count.
- ÷ 7 — Converts the day count into weeks plus a few leftover days.
- Days to go — How far the check date still sits before the due date.
Weeks, trimesters and terms at a glance
| Stage | Gestational weeks | Roughly days before due |
|---|---|---|
| First trimester | Weeks 0–13 | 187–280 days out |
| Second trimester | Weeks 14–27 | 91–186 days out |
| Third trimester | Weeks 28–40+ | 0–90 days out |
| Full term | Weeks 39–40 | 0–14 days out |
Days-out figures are from the start of each stage; your exact week changes by one day as the due date approaches.
This calculator answers a deceptively simple question — how far along am I — from the one number most pregnant people already know: their due date. Enter it and you get today's gestational age in weeks and days, your trimester, how far through the forty weeks you are, and how many days remain until your due date.
You can check the answer for today, or set any date to see where you stood earlier or will stand later. That makes it useful for matching a symptom, an appointment or a scan to the right week, and for planning around term.
Everything counts from the implied first day of your last period, which sits 280 days before your due date. That is the same reference your care team uses, so the weeks you see here line up with the weeks in your notes and on your scan reports.
How it works out your week
Pregnancy is dated in weeks from the last menstrual period rather than from conception. Because the due date is set at forty weeks — 280 days — after that period, you can reverse it: subtract 280 days from your due date to find day zero, then count forward to today.
The gap between day zero and your check date, divided by seven, gives completed weeks, and the remainder gives the extra days. So a count of 141 days reads as twenty weeks and one day.
The same number tells you the trimester. Weeks run to thirteen for the first, fourteen to twenty-seven for the second, and twenty-eight onwards for the third, so the week you are on also places you in the right stage.
A worked example
Suppose your due date is 1 December. Subtracting 280 days puts day zero — your implied last period — at 2 March, and that is the point the calculator counts forward from.
If today is 22 May, the span from 2 March is about eighty-one days, which the tool reads as eleven weeks and four days. The trimester label falls out automatically: under fourteen weeks, so you are in the first trimester.
For the other direction, the calculator measures from today to the due date. From 22 May to 1 December leaves a little over six months, or roughly 190 days to go, and the percentage shows you are about twenty-nine percent of the way through the forty weeks.
Reading the trimester and the percentage
Alongside the week, the calculator shows how far through the forty weeks you are as a percentage. Early on it moves quickly week to week; later it slows, which mirrors how the remaining time feels.
The trimester label tells you which block of care you are in, because screening tests, the anatomy scan and growth checks are each offered in a defined week range. Knowing your exact week is what tells you whether you are inside those windows.
Treat the percentage as orientation, not a countdown to a deadline. A pregnancy is considered term across several weeks, so being, say, ninety percent of the way through is not the same as being overdue; the days-to-due figure is the more practical one near the end.
Why a scan due date beats a period one
The whole result is only as good as the due date you feed in. If your due date came from an early ultrasound, it is usually accurate to within a few days, and the week this calculator reports is correspondingly reliable.
If it came only from the first day of a last period, and your cycles are irregular, the true week could differ. In that case the number is still useful, but expect your clinician to have adjusted dating at the scan.
Where a scan date and a period date disagree, the scan date wins in most services' guidelines. Use whichever due date your midwife or doctor confirmed so the weeks here match the weeks in your notes.
What to do near, at, and past your due date
As the days-to-go figure falls, the practical focus shifts to preparing for labour. Most babies arrive inside the window from thirty-seven to forty-one-plus weeks, so anywhere in that range is normal and not early or late.
Once you reach your due date the calculator reports zero days to go, and past it it counts days overdue. That is a prompt to stay in closer contact with your maternity unit rather than a reason to worry, because overdue is measured in small increments.
Whatever the week, some signs warrant a call rather than a calculation: reduced or changed movements, your waters breaking, bleeding, or regular painful contractions. Contact your provider promptly if any of these happen, at any gestational age.
How far along with twins or after IVF
This tool reads a single due date against a forty-week timeline, which fits a singleton pregnancy. A twin or higher-order pregnancy is usually timed to an earlier birth, often around thirty-five to thirty-eight weeks, so the percentage bar here is a rough guide rather than the target your team is working to.
After IVF the maths is actually more exact, because the transfer or egg-retrieval date fixes day zero precisely rather than relying on a remembered period. Enter the due date your fertility clinic confirms and the week count tracks to that same certainty.
In both cases the rule stays the same: use the due date your clinician has confirmed. The calculator faithfully converts whichever date you feed in, so the quality of the week it reports depends on the quality of that starting date.
Key terms
- Gestational age
- How far along a pregnancy is, counted in weeks and days from the last period.
- Implied LMP
- The last-period start date a due date points back to — 280 days before it.
- Trimester
- One of the three stages of pregnancy, each with its own schedule of checks.
- Days to go
- The number of days between today and your due date.
Pro tips
- Use your scan-confirmed due date for the most reliable week.
- Set the 'check on this date' field to map a past symptom or scan to the right week.
- Near the end, read days-to-due as the useful number rather than the percentage.
Common mistakes
- Feeding in a period-based due date when a scan date exists and differs.
- Assuming 'full term' means exactly forty weeks; it spans several.
- Panic on the due date itself — most births fall inside the surrounding window.
How far along calculator — your questions
How are you supposed to calculate how far along you are?
Count from the start of your last menstrual period, or work back from a due date. A due date is set at 280 days after that first day, so subtracting 280 days gives day zero and you then count the weeks forward to today. This calculator does the subtraction and the week count for you, and also tells you the trimester and how many days remain.
Is my week number exact?
The arithmetic is exact, but the starting date may not be. A week derived from a due date is only as good as that due date. A scan-based due date is usually accurate to a few days, so your week should match your notes. A period-based one can be off by several days if your cycles are irregular, which nudges the week either way.
Which week do the trimesters change?
The first trimester runs to the end of week thirteen, the second covers weeks fourteen through twenty-seven, and the third begins at week twenty-eight and continues until birth. These are the standard clinical boundaries, and this calculator labels them automatically from your week so you always know which stage of care you are in.
Can I use this without a due date?
This tool needs a due date because it works back from it. If you do not have one yet, use the pregnancy due date calculator first, entering your last period or a conception or transfer date, and it will produce the due date you then bring here. Once you have a scan, the confirmed due date is the best one to reuse across both tools.
What if the date is past my due date?
Then the calculator shows days overdue rather than days to go, which is normal and expected for many pregnancies. It is a cue to keep in closer touch with your maternity unit, not a reason to alarm, since care plans usually review you from around this point. If anything worries you, such as reduced movements, contact your provider whatever the count says.
Does this count from conception or my last period?
From the implied last period, which is the clinical convention and matches your care team. Because ovulation happens about two weeks after that first day, gestational age runs roughly two weeks ahead of the embryo's true, or conception, age. Keeping to the same reference avoids the confusion of two different week numbers.