Due Date Calculator.

How the Due Date Calculator works.

Due Date Calculator example using the starting values.

This Due Date Calculator example uses the starting inputs: First day of last menstrual period: 2025-01-01.

Result: 2025-10-08

Estimated due date from LMP.

What the result means

Estimate due date from last menstrual period. The Due Date Calculator result describes only the measurements and method shown; it is not a diagnosis or an individualized target.

Enter a consistent scenario

Use Due Date Calculator with values from one clearly defined scenario. The visible inputs are first day of last menstrual period. The 280-day estimate begins with the first day of the last menstrual period, not conception. Cycle length, uncertain dates, ultrasound findings, multiple pregnancy, and clinician assessment can change pregnancy dating. Check the unit, period, and meaning of each value before calculating; combining records from different dates can produce a precise-looking but unhelpful answer.

Follow the method

This page applies LMP + 280 days. The 280-day estimate begins with the first day of the last menstrual period, not conception. Cycle length, uncertain dates, ultrasound findings, multiple pregnancy, and clinician assessment can change pregnancy dating. First identify what each entered value represents, convert a percentage to the form required by the displayed formula, and retain intermediate precision. Then make a rough mental check of direction and size. Estimate due date from last menstrual period. The worked result is transparent arithmetic rather than an unshown lookup.

Use the result carefully

Read the output as an answer to the narrow question described by the fields, not as a prediction of every real-world outcome. The 280-day estimate begins with the first day of the last menstrual period, not conception. Cycle length, uncertain dates, ultrasound findings, multiple pregnancy, and clinician assessment can change pregnancy dating. For Due Date Calculator, compare results only when the measurement basis, time period, currency denomination, or grading convention is the same. This is general information, not a diagnosis, treatment target, or substitute for individual clinical care. Discuss symptoms, pregnancy dating, nutrition, exercise, or a concerning result with a qualified clinician.

Assumptions and boundaries

Before relying on Due Date Calculator, identify what its formula—LMP + 280 days—holds constant and what it does not observe. The 280-day estimate begins with the first day of the last menstrual period, not conception. Cycle length, uncertain dates, ultrasound findings, multiple pregnancy, and clinician assessment can change pregnancy dating. Its entries (first day of last menstrual period) define the full scope of this particular result. Do not turn a rounded display into more certainty than the entered data supports; use the official record or provider documentation where it controls.

Common mistakes and next steps

For Due Date Calculator, begin a review by comparing the displayed first day of last menstrual period against the source record. The 280-day estimate begins with the first day of the last menstrual period, not conception. Cycle length, uncertain dates, ultrasound findings, multiple pregnancy, and clinician assessment can change pregnancy dating. Typical mistakes are entering a percent as a decimal or vice versa, using an amount from the wrong time period, rounding before the final step, and treating an estimate as an official determination. Record the inputs and result if you need to compare scenarios later.

What the Due Date Calculator does not include.

This Due Date Calculator result is an estimate, not a diagnosis or treatment plan. Seek urgent care for concerning symptoms and discuss pregnancy, diet, sleep, or activity decisions with a qualified clinician.

Official context and guidance.

• CDC — Pregnancy (opens in a new tab)