Due Date Calculator: LMP, Conception & Reverse
Use this pregnancy due date calculator to calculate your due date by last period (LMP), conception date, or reverse (estimate conception from due date).
Pregnancy Due Date Calculator
If you’re unsure, choose Last Period (LMP).
Select the first day you started bleeding in your last period.
If unsure, keep 28. This is used to adjust estimates when using LMP.
Calculate Your Pregnancy Due Date (EDD)
This due date calculator (also called a pregnancy due date calculator or baby due date calculator) helps you calculate due date and estimate your expected due date (EDD). You can calculate using your last menstrual period (LMP), a known conception date, or use a reverse / backwards due date calculator if you already have an EDD and want to estimate conception timing. Results are estimates and may vary based on cycle length and individual factors.
If you’re searching for an estimated due date calculator or an accurate due date calculator, remember that the most accurate dating is often confirmed by early ultrasound—especially if your cycles are irregular.
Due Date Calculation Methods
| Method | Calculation Rule | Notes |
|---|---|---|
| Last Period (LMP) | LMP + 280 days (adjusted by cycle length) | Most common method; also called a due date calculator based on last period |
| Conception Date | Conception + 266 days | Helpful if conception/ovulation date is known (due date calculator by conception date) |
| Reverse | Due Date - 266 days | Reverse due date calculator to estimate likely conception timing (approx.) |
How to Use This Due Date Calculator
- 1Choose a method: Last Period (LMP), Conception Date, or Reverse.
- 2Enter the relevant date.
- 3If using Last Period (LMP), adjust cycle length if your cycle is typically longer or shorter than 28 days.
- 4Click Calculate to see your estimated due date and pregnancy timeline.
Due Date FAQs
How accurate is a due date?
A due date is an estimate. Many babies are born within about 2 weeks before or after the estimated due date. If your cycles are irregular, an early ultrasound is often more accurate than an LMP due date calculator (due date calculator based on last period).
How is due date calculated?
Most commonly, due date is calculated from the first day of your last menstrual period (LMP) using a standard 280-day estimate (40 weeks), with adjustments for cycle length. If you know conception/ovulation timing, you can calculate due date from conception by adding about 266 days.
How does reverse due date calculation work?
If you enter a due date, the calculator subtracts about 266 days to estimate conception timing. This reverse or backwards due date calculator does not identify an exact day—fertile timing can vary by a few days.
Can I calculate my due date from my last period or conception date?
Yes. You can calculate due date from last period (LMP) or calculate my due date from conception if you know your conception/ovulation date. Both methods provide an estimated due date (EDD).
Medical Disclaimer
Note: This calculator provides an estimate based on standard medical formulas. It is not a substitute for professional medical advice. Please consult a qualified healthcare provider for clinical dating and medical care.