Due Date Calculator
Enter your last period date or conception date to find your estimated due date, current pregnancy week, and trimester.
Disclaimer: The results provided by this tool are estimates for informational purposes only and do not constitute medical advice. Please consult a healthcare professional for personal health decisions.
How the due date estimate is produced
The due date calculator applies Naegele's rule, the standard obstetric convention that adds 280 days — forty weeks — to the first day of the last menstrual period. This figure assumes a regular 28-day cycle with ovulation on day 14, so the 280 days actually represent about 266 days of true gestation plus 14 days of pre-conception time. If you know your conception date or the date of a confirmed ovulation, the calculator can add 266 days to that instead, which gives a tighter estimate for people with irregular or non-standard cycles.
From the estimated due date, the tool works backwards and forwards to label pregnancy weeks and trimester boundaries. Each week begins exactly seven days after the previous one, and the current week is computed against today's date on your device. Because the math is purely calendar-based, the output is only as accurate as the input: a misremembered last period date or an unusually long cycle will shift every downstream milestone. This is an informational estimate, not a clinical assessment — your healthcare provider can refine dating with an early ultrasound, which is considered the most accurate method.
When to use the due date calculator
The most common use is a first rough timeline during early pregnancy, before an ultrasound appointment is available. Seeing the projected trimester boundaries, viability window, and delivery month helps people plan conversations with employers, schedule travel, and think through logistical decisions like childcare and leave. Some users also run the calculator during conception planning to understand when a given ovulation would produce a baby born in a preferred season, or to check whether a late period could have produced a plausible pregnancy timeline worth testing.
Edge cases are worth keeping in mind. Assisted reproduction cycles use the embryo transfer or retrieval date rather than the last period, and cycles longer or shorter than 28 days need manual adjustment — add or subtract the difference from 28 to the 280-day total. Only about 5% of babies arrive on the exact predicted day, and most births cluster within a two-week window on either side. For anything beyond general scheduling — such as concerns about preterm labour, post-term monitoring, or high-risk pregnancy — consult a healthcare provider for medical guidance rather than relying on this estimate alone.