Due Date Calculator
Estimated due date from LMP.
The standard 28-day cycle uses 280 days from LMP.
Estimated due date
Introduction
Estimate a due date from the first day of your last menstrual period and usual cycle length. A first-trimester ultrasound can establish or confirm gestational age more accurately.
What is Due Date Calculator?
The standard estimate is 280 days (40 weeks) from the first day of the LMP for a 28-day cycle. The calculator adjusts that calendar estimate for the usual cycle length you enter. Your clinician may confirm or revise the date using early ultrasound or other information.
Definition: Due Date Calculator estimates an expected due date from the first day of the last menstrual period and usual cycle length.
Formula
EDD = LMP + 280 days (Naegele's rule)
Calculation steps
- The core formula: EDD = LMP + 280 days (Naegele's rule)
- Enter your values in the fields above — units and assumptions are under your control.
- The Daily Tools computes the result instantly in your browser using JavaScript.
- Review the result panel for the primary output and supporting breakdown values.
Worked example
Example: estimate a due date from LMP
Inputs: First day of LMP = 1 January 2026, Usual cycle length = 28 days
- Start with the first day of the last menstrual period.
- Use 280 days (40 weeks) for the standard 28-day-cycle estimate.
- Adjust the calendar estimate when a different usual cycle length is entered.
The displayed date is an estimated due date, not a prediction of the day birth will occur.
Use cases
- Getting an initial estimated due date from a known LMP
- Understanding how a usual cycle length changes a calendar estimate
- Keeping an estimated date for personal planning before discussing it with a clinician
Advantages
- Browser-based processing — entered values and selected files are not sent to our servers
- No account required
- Instant results with a clean, readable interface
- Transparent formula shown on this page
Limitations
- Only a small proportion of births occur on the exact estimated due date.
- Irregular cycles, uncertain LMP, assisted reproduction, and clinical findings can change the best estimate.
- This calculator does not replace prenatal care, ultrasound, or medical advice.
Frequently asked questions
- Why is the due date based on my last period rather than conception?
- Pregnancy dating commonly starts from the first day of the LMP because conception timing is often uncertain. The standard LMP-based estimate is 280 days.
- Can an ultrasound change my due date?
- An early ultrasound can establish or confirm gestational age more accurately, particularly when the LMP is uncertain or cycles are irregular.
- Does the due date mean my baby will be born that day?
- No. It is an estimated date used to track gestational age and care; birth can occur before or after it.
- Is the Due Date Calculator free to use?
- Yes. Due Date Calculator on The Daily Tools is completely free, requires no account, and runs entirely in your browser.
- Does The Daily Tools store my inputs?
- No. Your numbers and text never leave your device. The Daily Tools has no backend database for calculator inputs.
- Who should use the Due Date Calculator?
- Anyone who needs a clear health and fitness calculation and wants to check the assumptions used.
- How accurate is the Due Date Calculator?
- Results follow the standard formula shown on this page. They are estimates for planning — not a substitute for professional medical advice.
- Can I use the Due Date Calculator on mobile?
- Yes. The Daily Tools is fully responsive and works on phones, tablets, and desktops.
Sources & references
Key points
- Due Date Calculator is a free, browser-based calculator for estimated due date from LMP.
- Formula: EDD = LMP + 280 days (Naegele's rule)
- Private, browser-only processing
- Private, browser-based processing