Pregnancy Calculator – Estimate Your Due Date and Weeks
Calculate how far along you are, when the baby is due and which trimester you are in.
About the Pregnancy Calculator
What is the Pregnancy Calculator?
A pregnancy calculator uses the first day of your last period to estimate your current gestational age, trimester and due date.
Why use this calculator?
Knowing your due date guides antenatal care: when to book scans, when results come in and how to plan your pregnancy timeline.
How to use it
- Enter the first day of your last menstrual period.
- Enter your average cycle length if it is not 28 days.
- Read your gestational age, trimester and estimated due date.
Formula
Due date = LMP + 280 days, adjusted for cycle length.
Only about 5% of babies arrive exactly on the due date. It is an estimate — yours will come in the weeks around it.
Frequently Asked Questions
Why is pregnancy counted from before conception?
Tradition and convenience: the LMP is easy to recall, and the 40-week count starts two weeks before actual conception.
What happens if my cycle is irregular?
Estimates get less reliable. An early ultrasound dating scan is usually the most accurate way to pin the date instead.
Does it account for leap years?
Yes. The date logic follows the Gregorian calendar, including leap years and differing month lengths.
Are weekends and holidays excluded?
Only if the calculator says so. By default, results count every calendar day; use a business-day option where available.
Which time zone is used?
Calculations use whole calendar dates and are time-zone independent unless a time-of-day is involved.
Is this a medical diagnosis?
No. This tool provides general wellness information only. It is not a substitute for evaluation by a qualified healthcare professional.
Why do results differ from my doctor's measurements?
Clinical measurements use calibrated equipment and professional technique. Home estimates rely on formulas and self-reported values, so small differences are normal.
How often should I recalculate?
Recheck after meaningful changes such as weight gain or loss, a new workout routine, or every few months to track trends over time.
Do these formulas apply to everyone?
Most population formulas are less accurate for athletes, pregnant people, very young children and the elderly. Use them as a general guide.
Is this calculator free to use?
Yes. Every calculator on this site is completely free, with no hidden fees, no subscriptions and no limits on how many times you can use it.