Calculator Comparison

Due Date Calculator vs Pregnancy Week Calculator

Not sure which calculator to use? Here's a side-by-side comparison of the Due Date Calculator and Pregnancy Week Calculator to help you pick the right one for your needs.

Due Date Calculator

Pregnancy & Baby

Calculate your estimated due date using your last menstrual period, conception date, or IVF transfer date.

What you enter

Calculate Based On
Date

What you get

Estimated Due Date(primary)
Estimated Conception Date
Current Week of Pregnancy
Days Until Due Date

Use Due Date Calculator

Pregnancy Week Calculator

Pregnancy & Baby

Calculate exactly how many weeks and days pregnant you are based on your last menstrual period or estimated due date.

What you enter

First Day of Last Period

What you get

Weeks and Days Pregnant(primary)
Current Trimester
Estimated Due Date
Pregnancy Progress

Use Pregnancy Week Calculator

Key Differences

Feature	Due Date Calculator	Pregnancy Week Calculator
Category	Pregnancy & Baby	Pregnancy & Baby
Inputs	2 required fields	1 required fields
Outputs	4 results	4 results
Chart	No chart	No chart
FAQs	3 answered	3 answered

Input Comparison

Only in Due Date Calculator

Calculate Based On
Date
Average Cycle Length (for LMP)

Only in Pregnancy Week Calculator

First Day of Last Period

Which Calculator Should You Use?

Use the Due Date Calculator if you need to:

Calculate estimated due date
When you know your calculate based on and date

Use the Pregnancy Week Calculator if you need to:

Calculate weeks and days pregnant
When you know your first day of last period

Frequently Asked Questions

How is the due date calculated?

The most common method (Naegele's rule) adds 280 days (40 weeks) to the first day of your last menstrual period. Adjustments are made for cycle lengths that differ from 28 days.

How accurate is a due date?

Only about 5% of babies are born on their exact due date. Most babies arrive within 2 weeks before or after the due date. First-time mothers tend to deliver slightly later.

How do I count pregnancy weeks?

Count from the first day of your last menstrual period (LMP). If your LMP was January 1 and today is February 12, you're about 6 weeks pregnant. Your doctor counts the same way.

Why does pregnancy start before conception?

Pregnancy is dated from the LMP because most women know this date reliably. Conception usually occurs about 2 weeks later. This is why at 4 weeks pregnant, the embryo is about 2 weeks old.

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Bottom Line

Choose the Due Date Calculator if you need to calculate estimated due date. Use the Pregnancy Week Calculator if you need to calculate weeks and days pregnant. Both calculators are free and require no sign-up.

Use Due Date Calculator Use Pregnancy Week Calculator

Feature

Due Date Calculator

Pregnancy Week Calculator