Gestational Age Calculator
Weeks pregnant from LMP.
Enter your values
Enter the days since last period you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Gestational age
- 18 weeks 0 days
- Trimester
- Second
- Days remaining to 40 weeks
- 154
- Percent of pregnancy complete
- 45%
- Estimated fetal age
- 16 weeks
Quick answer
Gestational age counts from the first day of your last period, so it runs about two weeks ahead of conception.
At a glance
| What it does | Weeks pregnant from LMP. |
|---|---|
| Category | Health |
| Inputs needed | Days since last period |
| Main output | Gestational age |
| Cost | Free — no sign-up, no download |
How to use the Gestational Age Calculator
- 1Count days since the first day of your last period.
- 2Enter that number.
- 3Read your gestational age and trimester.
Inputs explained
- Days since last period
- Enter the days since last period you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Days since last period126
Results
- Gestational age18 weeks 0 days
- TrimesterSecond
- Days remaining to 40 weeks154
- Percent of pregnancy complete45%
- Estimated fetal age16 weeks
Frequently asked questions
Why is fetal age two weeks less?
Ovulation usually happens about 14 days after your period starts.
Is an ultrasound more accurate?
Yes, especially a first trimester dating scan.
What do I need to enter into the Gestational Age Calculator?
Just 1 value: days since last period. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Gestational Age Calculator work out the answer?
Gestational age counts from the first day of your last period, so it runs about two weeks ahead of conception. The working is shown step by step so you can verify the result by hand.
Is the Gestational Age Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.