Pregnancy Calculator
Weeks pregnant and trimester.
Use your usual cycle length; 28 days is the standard assumption.
Estimated gestational age
35
weeks6 days · Third trimester
Introduction
Estimate gestational age and due date from the first day of your last menstrual period. An early ultrasound or clinician’s estimate may be more accurate. This result is an estimate based on the information provided. It is not a diagnosis and may not reflect individual medical circumstances.
What is Pregnancy Calculator?
This calculator uses the first day of your last menstrual period (LMP) to estimate how many weeks and days pregnant you are. It also shows an estimated due date. These are calendar estimates, not a substitute for prenatal care or ultrasound dating.
Definition: Pregnancy Calculator estimates gestational age, trimester, and an estimated due date from the first day of the last menstrual period.
Formula
Weeks pregnant from LMP; trimester by week count
Calculation steps
- The core formula: Weeks pregnant from LMP; trimester by week count
- Enter your values in the fields above — units and assumptions are under your control.
- The Daily Tools computes the result instantly in your browser using JavaScript.
- Review the result panel for the primary output and supporting breakdown values.
Worked example
Example: estimate gestational age from LMP
Inputs: First day of LMP = 1 January 2026, Usual cycle length = 28 days
- Count elapsed days from the first day of the last menstrual period.
- Convert completed days into weeks and remaining days.
- Add 280 days to the LMP for the standard estimated due date.
The result is a calendar estimate; early ultrasound and clinical care may establish a different due date.
Use cases
- Understanding the approximate gestational week from a known LMP
- Keeping a personal calendar of an estimated due date
- Preparing questions to discuss with a midwife, obstetrician, or other clinician
Advantages
- Browser-based processing — entered values and selected files are not sent to our servers
- No account required
- Instant results with a clean, readable interface
- Transparent formula shown on this page
Limitations
- The result depends on an accurate LMP and a reasonably regular cycle.
- First-trimester ultrasound is the most accurate method to establish or confirm gestational age.
- This calculator does not assess pregnancy health, symptoms, fetal growth, or emergency concerns.
Frequently asked questions
- How many weeks is a typical pregnancy?
- A typical pregnancy is estimated as 40 weeks, or 280 days, from the first day of the LMP. The due date is an estimate, not a prediction of the exact birth date.
- What if I do not know my last period date?
- A clinician can use your history and an ultrasound examination to help estimate gestational age and due date.
- Does a different cycle length change the result?
- It can. This calculator adjusts the standard estimate when you enter a usual cycle length from 21 to 45 days.
- Is the Pregnancy Calculator free to use?
- Yes. Pregnancy Calculator on The Daily Tools is completely free, requires no account, and runs entirely in your browser.
- Does The Daily Tools store my inputs?
- No. Your numbers and text never leave your device. The Daily Tools has no backend database for calculator inputs.
- Who should use the Pregnancy Calculator?
- Anyone who needs a clear health and fitness calculation and wants to check the assumptions used.
- How accurate is the Pregnancy Calculator?
- Results follow the standard formula shown on this page. They are estimates for planning — not a substitute for professional medical advice.
- Can I use the Pregnancy Calculator on mobile?
- Yes. The Daily Tools is fully responsive and works on phones, tablets, and desktops.
Sources & references
Key points
- Pregnancy Calculator is a free, browser-based calculator for weeks pregnant and trimester.
- Formula: Weeks pregnant from LMP; trimester by week count
- Private, browser-only processing
- Private, browser-based processing