Pregnancy Calculator
Estimate your pregnancy due date, current pregnancy week and key dates using the first day of your last menstrual period.
Enter the first day of your most recent menstrual period.
The standard estimate uses a 28-day cycle. Adjust this if your cycle is usually longer or shorter.
The calculator estimates pregnancy dates using a typical 40-week pregnancy and adjusts the estimate for your cycle length.
How the Pregnancy Calculator Works
A typical pregnancy is estimated as approximately 40 weeks from the first day of the last menstrual period (LMP). The estimated due date is therefore calculated by adding about 280 days to the LMP.
If your average menstrual cycle differs from 28 days, the calculator adjusts the estimated due date by the difference in cycle length.
How to Use the Pregnancy Calculator
Enter Your Last Menstrual Period
Select the first day of your most recent menstrual period.
Enter Your Cycle Length
Use 28 days if your cycle is close to the standard 28-day cycle, or enter your usual average cycle length.
Calculate
The calculator estimates your due date, pregnancy progress, conception date and trimester milestones.
Pregnancy Date Estimates
The estimated conception date is approximately two weeks after the first day of the last menstrual period for a standard cycle. The exact timing of ovulation and conception can vary.
The estimated due date is a planning estimate rather than a guaranteed delivery date. Only a relatively small proportion of babies are born exactly on their estimated due date.
Understanding Pregnancy Trimesters
First Trimester
Generally covers the early weeks of pregnancy through approximately week 13.
Second Trimester
Generally covers approximately weeks 14 through 27.
Third Trimester
Generally begins around week 28 and continues through delivery.
Important Information
This calculator provides an estimate for general informational purposes. Pregnancy dating can be affected by irregular cycles, uncertain LMP dates, variable ovulation and other factors.
Healthcare professionals may use ultrasound and other clinical information to establish or revise pregnancy dating. Speak with your healthcare professional for personal medical guidance, pregnancy dating or concerns about your pregnancy.
Frequently Asked Questions
How accurate is the estimated due date?
The estimated due date is a planning estimate. The actual delivery date can occur before or after the estimated date.
What if my menstrual cycle is not 28 days?
Enter your usual average cycle length. The calculator adjusts the estimated due date based on the difference from a 28-day cycle.
Can I use this calculator if my cycles are irregular?
You can use it for a rough estimate, but irregular cycles can make LMP-based dating less precise. A healthcare professional can provide more appropriate pregnancy dating.
When does pregnancy counting start?
Pregnancy is conventionally dated from the first day of the last menstrual period, which is approximately two weeks before conception in a typical cycle.
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