Free Online Pregnancy Calculator
Determine your estimated due date (EDD), track your current week of pregnancy, view trimester progress, and count down the days until your baby's arrival using your last menstrual period. This accurate pregnancy calculator supports both US Imperial units and UK/EU Metric units, aligning with key standards from the CDC, NHS, and WHO.
Pregnancy Assessment Results
Timeline & Key Dates
| Milestone / Event | Date | Description |
|---|---|---|
| Estimated Conception Date | — | Estimated date of ovulation and fertilization (adjusted for cycle length) |
| First Trimester Ends | — | Completion of the 13th week of pregnancy (13 weeks, 6 days) |
| Second Trimester Ends | — | Completion of the 27th week of pregnancy (27 weeks, 6 days) |
| Estimated Due Date (EDD) | — | Completion of 40 weeks (280 days from adjusted LMP) |
How Gestational Age & Due Date are Calculated
Our free online Pregnancy Calculator provides a simple and accurate way to estimate your due date, track milestones, and count down the days until your baby's arrival. By using this tool, you can monitor your baby's development week by week and understand the timeline of your pregnancy.
In clinical practice, gestational age and pregnancy progression are standardly calculated from the first day of your Last Menstrual Period (LMP). While ovulation and conception typically happen about 14 days later (for a standard 28-day cycle), this standard convention is widely used by health authorities because the exact date of conception is rarely known with certainty.
For an average 28-day cycle, the Estimated Due Date (EDD) is calculated by adding 280 days (40 weeks) to the first day of the LMP. This estimated due date aligns with the standard Naegele's rule.
However, menstrual cycles vary significantly between individuals. For accurate menstrual cycle tracking, if your average cycle length is shorter or longer than 28 days, ovulation happens earlier or later. This shifts your fertile window and safe ovulation window boundaries. Our accurate calculator accounts for this variation by adjusting both the due date and gestational age to match your specific cycle profile:
The Adjusted LMP is computed as follows:
Gestational Age (Days) = Today's Date - Adjusted LMP
This cycle adjustment provides a much more accurate estimate of fetal age, trimesters, and progress, especially for cycles that consistently diverge from the standard 28-day duration.
How to Use This Pregnancy Calculator
- Select your LMP Date: Input the calendar date representing the first day of bleeding of your last menstrual cycle.
- Select your Average Cycle Length: Choose your normal cycle duration (the number of days from the start of one period to the start of the next). If you aren't sure, 28 days is the default and average value.
- Click the Calculate button to process the dates and reveal the results.
- Use the Clear button to wipe the inputs and start fresh.
Pregnancy Milestones and Trimesters Reference Table
Pregnancy is standardly divided into three trimesters, each characterized by specific developmental stages for the fetus and anatomical changes for the mother.
| Trimester | Weeks Range | Major Fetal Development Milestones |
|---|---|---|
| Trimester 1 | Weeks 1 – 13 (Days 0–97) | Fertilization and implantation occur. The embryo develops vital organs, including the heart, brain, and spinal cord. Fingerbuds, toes, and facial features begin to form. By the end of the trimester, all major body systems are present. |
| Trimester 2 | Weeks 14 – 27 (Days 98–195) | Fetal movement (quickening) becomes noticeable. The baby's sex can often be identified via ultrasound. Lungs grow rapidly, and taste buds, hair, eyelashes, and fingernails develop. The fetus can hear sounds outside the womb. |
| Trimester 3 | Weeks 28 – 40+ (Days 196–280+) | Rapid weight gain and growth for both mother and fetus. The baby's brain undergoes massive development. The lungs mature and prepare for breathing. The fetus shifts into a head-down position in preparation for birth. |
* Note: Gestational age measures pregnancy from the LMP. Delivery between 37 and 42 weeks is medically considered full term.
Frequently Asked Questions
How accurate is a free online pregnancy calculator?
A free online pregnancy calculator provides a highly accurate estimate of your due date when based on the first day of your last menstrual period (LMP) and your average cycle length. However, only an early ultrasound scan (dating scan) performed by a healthcare professional (in accordance with NHS and CDC guidelines) can confirm your gestational age with high clinical accuracy.
What is the difference between gestational age and conception age?
Gestational age measures the age of the pregnancy starting from the first day of your Last Menstrual Period (LMP). In contrast, conception age (fetal age) measures the actual age of the growing fetus from the date of fertilization, which typically occurs about two weeks after the LMP. Medical providers (including the WHO and CDC) standardly use gestational age for tracking pregnancy milestones.
How do cycle length variations affect the due date calculation?
The standard Naegele's rule assumes a 28-day menstrual cycle where ovulation occurs on day 14. If your cycle is shorter or longer (e.g., 24 or 35 days), ovulation happens earlier or later, respectively. Our accurate pregnancy calculator adjusts the LMP by adding or subtracting the difference from 28 days to ensure a more precise estimated due date (EDD) for users of both US Imperial units and UK/EU Metric units.
When is a pregnancy considered full-term according to NHS and WHO standards?
According to WHO classifications and NHS standards, a pregnancy is considered "full-term" when it reaches 39 weeks (between 39 weeks 0 days and 40 weeks 6 days). Deliveries between 37 weeks and 38 weeks 6 days are termed "early term," while deliveries from 41 weeks to 41 weeks 6 days are "late term."
Related Health Tools
Once you have calculated your estimated due date, check your menstrual cycle details using our Period Calculator, find your conception window using the Pregnancy Conception Calculator, manage gestational weight targets using the Pregnancy Weight Gain Calculator, or track your general body measurements with the BMI Calculator.