Pregnancy Gestational Age Calculator
Work out how many weeks and days pregnant you are today, plus your estimated due date and trimester, from your LMP, conception date, IVF transfer date, or a known due date.
Pregnancy Progress
This bar is a visual guide against a standard 40-week (280-day) pregnancy — actual delivery timing varies.
Key Dates
Trimester Reference
Pregnancy Gestational Age Calculator
Our Gestational Age Calculator works out how many weeks and days pregnant you are today, using your last menstrual period (LMP), conception date, IVF embryo transfer date, or an already-confirmed due date. Unlike a simple due date calculator, this tool focuses on where you are right now in the pregnancy — your current gestational age, trimester, and how much of the standard 40 weeks has passed.
What Is Gestational Age?
Gestational age is the standard clinical way of dating a pregnancy, measured in completed weeks and days from the first day of your last menstrual period (LMP) — not from the date of conception. Because ovulation and conception typically occur around two weeks after the start of your last period, gestational age runs about two weeks ahead of “fetal age” (the age measured from conception itself). This is why a newly confirmed pregnancy is often already dated at around 4–5 weeks gestational age.
How Each Dating Method Works
- Last menstrual period (LMP): The standard method. Gestational age is simply the number of days since the first day of your last period, converted to weeks and days.
- Conception date: If you know your conception date precisely (for example, from ovulation tracking), we add 14 days to convert it to an LMP-equivalent date, then calculate gestational age from there.
- IVF embryo transfer: For IVF, the embryo’s age at transfer is known precisely. Gestational age at the moment of transfer is conventionally 14 days plus the embryo’s age — so a Day 5 blastocyst transfer is dated as 2 weeks 5 days gestational age on the transfer date itself, and a Day 3 transfer as 2 weeks 3 days.
- Known due date: If you already have a due date confirmed by ultrasound or your care provider, we work backwards using the standard 280-day pregnancy length to find your LMP-equivalent date and current gestational age.
Estimated Due Date (Naegele’s Rule)
The estimated due date shown by this calculator uses the conventional 280-day (40-week) pregnancy dating formula: LMP-equivalent date plus 280 days. This is the conventional formula used for pregnancy dating, though your midwife or doctor may adjust your due date based on your dating ultrasound, particularly if your cycle length differs from the assumed 28 days.
Trimester Reference
| Gestational Age Range | Trimester |
|---|---|
| 0 weeks 0 days – 13 weeks 6 days | First trimester |
| 14 weeks 0 days – 27 weeks 6 days | Second trimester |
| 28 weeks 0 days onward | Third trimester |
These boundaries are a commonly used approximation for patient information purposes; exact trimester cut-offs can vary slightly between sources and are not a precise clinical threshold.
How to Use This Calculator
- Choose your dating method – LMP, conception date, IVF transfer, or a known due date.
- Enter the relevant date – and, for IVF, the embryo’s age at transfer.
- Check or adjust the “as of” date – this defaults to today, but you can calculate gestational age for any date.
- Click Calculate Gestational Age to see your results, due date, and trimester.
Frequently Asked Questions
How is gestational age different from fetal age?
Gestational age is counted from the first day of your last menstrual period and is the standard measure used by midwives and doctors. Fetal (or conceptional) age is counted from the actual date of conception and is typically about two weeks less than gestational age, since ovulation and conception usually occur roughly two weeks into the menstrual cycle.
Why does my IVF transfer date give a gestational age of more than a few days?
Gestational age is always expressed on the LMP-equivalent timeline, not counted from the transfer date itself. A Day 5 blastocyst transfer is conventionally dated as 2 weeks 5 days gestational age on the day of transfer, because this aligns IVF pregnancies with the same dating scale used for natural conceptions. Day 3 transfers are dated as 2 weeks 3 days, and Day 6 transfers as 2 weeks 6 days.
How accurate is this calculator compared to an ultrasound dating scan?
This calculator uses standard obstetric dating formulas and is a reliable estimate when your cycle is regular and your dates are accurate. However, a first-trimester dating ultrasound can provide a more accurate estimate of gestational age and due date, particularly if your cycles are irregular or your LMP date is uncertain. If your ultrasound dating differs from your LMP-based dating by more than about a week, your care provider may use the ultrasound date instead.
What if I don’t know the exact first day of my last period?
If your LMP date is uncertain or your cycles are irregular, results from this calculator will be less reliable. In this situation, a dating ultrasound — usually offered in early pregnancy — can provide a more accurate estimate of gestational age and due date. You can also use the “known due date” option here if your care provider has already given you a confirmed due date.
Does this calculator apply to twin or multiple pregnancies?
Gestational age is calculated the same way for singleton and multiple pregnancies. However, twin and multiple pregnancies often deliver earlier than the standard 40-week estimate, so the due date shown here should be treated as a starting reference point rather than an expected delivery date. Your care provider will give you tailored guidance based on your specific pregnancy.