Pregnancy Due Date Calculator

Estimate a pregnancy due date from the date and cycle assumptions entered. Enter your own values below to see estimated due date and check the method behind it.

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Your inputs

Change the example values to match your situation.

Your result

Let’s work it out.

Fill in your inputs and select Calculate.
Your result and breakdown will appear here.

How this calculator works

Estimated due date = period start + 280 days + (usual cycle length − 28).

Before you use the result

  • Cycle-based estimate only. Ultrasound and clinical assessment can revise pregnancy dating.

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What is Pregnancy Due Date Calculator?

Pregnancy Due Date Calculator helps you estimate a pregnancy due date from the date and cycle assumptions entered.

The main result is estimated due date. The formula, example and assumptions below explain how to interpret it.

How to use Pregnancy Due Date Calculator

Use the example to get familiar with the form, then enter your own figures. Any rates in the example are illustrative. Check the field labels and units before calculating.

  1. Gather first day of last menstrual period and usual cycle length. Use values from the same situation or reporting period.
  2. Replace the example first day of last menstrual period with your own value, then complete the other fields. Check the displayed units.
  3. Select Calculate and read estimated due date. Change one input and calculate again to compare a second scenario. Reset restores the original example.
  • Select the first day of last menstrual period as a calendar date. The example uses 2026-07-20.
  • Enter usual cycle length, at least 21 and at most 45. Use a whole number.

Pregnancy Due Date Calculator: a worked example

With the inputs below, the result is 2027-04-26 (estimated due date). Follow the example, then replace these illustrative values with your own.

Example inputs and output
Input or outputExample value
First day of last menstrual period2026-07-20
Usual cycle length28
Estimated due date2027-04-26

Understanding the Pregnancy Due Date result

The main output is estimated due date. It applies to the inputs and operation you selected.

Displayed results use a readable number of decimal places. When checking a result by hand, keep extra precision until the last step. To compare scenarios, change one input at a time and keep the others fixed.

Pregnancy Due Date Calculator: assumptions and common mistakes

A useful estimate starts with the right inputs. Check the following assumptions and limits before applying the result to your situation.

  • Cycle-based estimate only. Ultrasound and clinical assessment can revise pregnancy dating.
  • Health estimates are context-dependent. Age, pregnancy, illness, medication and individual measurements can affect interpretation; these tools do not diagnose a condition.

For wider guidance, visit World Health Organization. The formula and scope of this specific tool are stated on this page.

Pregnancy Due Date Calculator FAQs

What does Pregnancy Due Date Calculator calculate?

Pregnancy Due Date Calculator helps you estimate a pregnancy due date from the date and cycle assumptions entered. Its main output is estimated due date.

What inputs do I need for Pregnancy Due Date Calculator?

You need first day of last menstrual period and usual cycle length. Use the field labels and units to match your figures to the formula.

Which formula does Pregnancy Due Date Calculator use?

Estimated due date = period start + 280 days + (usual cycle length − 28).

What is a worked example for Pregnancy Due Date Calculator?

Example inputs: First day of last menstrual period: 2026-07-20; Usual cycle length: 28. The result is 2027-04-26 (estimated due date).

How should I enter first day of last menstrual period?

Select the first day of last menstrual period as a calendar date. The example uses 2026-07-20.

How do I choose usual cycle length?

Enter usual cycle length, at least 21 and at most 45. Use a whole number. The example uses 28; replace it if your circumstances differ.

How should I read estimated due date?

The main output is estimated due date. It applies to the inputs and operation you selected.

Why might my Pregnancy Due Date Calculator result differ from my records?

Cycle-based estimate only. Ultrasound and clinical assessment can revise pregnancy dating. Differences in entered values, units or rounding can also change the comparison.

Can I compare two scenarios in Pregnancy Due Date Calculator?

Yes. Note your first estimated due date, change first day of last menstrual period or another input, and select Calculate again. Editing a field clears the old result so it is not mistaken for a new calculation.

Is Pregnancy Due Date Calculator free, and where are my inputs calculated?

This calculator is free to use without signing in. Its formula runs in your browser; calculator inputs are not sent to a calculation API. The inputs reset to the example values when you reset the form or start a fresh page.