Due Date Calculator

Due date calculator based on LMP (last menstrual period)

This due date calculator estimates your pregnancy due date using the most common real-world method: the first day of your last menstrual period (LMP). Most people search for a “due date calculator” because they want a quick, practical estimate they can put on a calendar. That is exactly what this tool is for. It gives you an estimated due date, your current gestational age (weeks and days), your trimester, and a few milestone dates that help with planning.

The estimate is based on a 40-week pregnancy length measured from LMP. That is the standard convention used in many clinics and pregnancy tracking tools because LMP is usually easier to recall than the exact day of conception. If your cycle is not the “textbook” 28 days, this calculator lets you adjust the estimate using your typical cycle length. A longer cycle usually means ovulation happens later, so the due date is usually a bit later as well. A shorter cycle often means ovulation is earlier, so the due date may be earlier.

To use it, enter the first day of your last period in YYYY-MM-DD format. If you know your typical cycle length, enter it too. If you leave cycle length blank, the calculator assumes 28 days. When you click calculate, you will see your estimated due date first. Under that, you will see how far along you are today in weeks and days, plus how many days remain until the estimate. Milestone dates are included to give you simple, calendar-friendly checkpoints, but they are still estimates, not medical appointments.

Assumptions and how to use this calculator

• This calculator is designed for LMP-based dating only. It does not estimate due date from ultrasound measurements, IVF transfer dates, or known conception dates.
• It assumes a typical pregnancy length of 280 days (40 weeks) from LMP, then adjusts the estimate by the difference between your cycle length and 28 days.
• If your cycle length is unknown or varies a lot, use the default 28 days and treat the result as a rough planning estimate.
• Cycle length adjustment is most meaningful when your cycles are consistently shorter or longer than average, not when they change month to month.
• All milestone dates shown are planning aids and can differ from medical guidance based on your personal history, symptoms, and clinical assessment.

Common questions

Is the due date from this calculator exact?

No. It is an estimate. Even with perfect inputs, many pregnancies do not end on the estimated due date. This tool gives you a reasonable target date for planning and a consistent way to track gestational age.

What if I do not remember the exact first day of my last period?

Use your best estimate. If you only know the approximate week, choose a date that is most plausible and treat the output as a range rather than a single fixed truth. If your estimate changes later, update the input and recalculate.

Why does cycle length change the result?

The standard 40-week method assumes ovulation around day 14 of a 28-day cycle. If your typical cycle is longer, ovulation often happens later, which shifts the estimated due date later. If your cycle is shorter, the estimate shifts earlier. This is a simple adjustment and will not be perfect for everyone.

What if I have irregular cycles?

If your cycle length varies widely, the cycle length adjustment can be misleading. In that case, leave cycle length blank and use the default. If you later get clinical dating information, use that for medical decisions.

Does this apply to IVF or tracked ovulation?

Not reliably. IVF and precisely tracked ovulation are different dating inputs, and the correct method is not the same as LMP dating. This calculator is intentionally locked to the LMP method to keep it simple and consistent for the most common search intent.