OB Wheel (Pregnancy Calculator)

Welcome users!

This site is designed for mobile devices, but can be viewed on any size screen!


About this app

This is a Progressive Web App version of my Android app, "OB Wheel".

Works best on Google Chrome.

For Google Chrome on Android, the webapp can be installed on your mobile device like a normal app by going to "Add to Desktop" in your menu. You may be automatically prompted to install the app by the browser. If installation does not work correctly, you can just bookmark this page and use it as-is.

As far as I can find, this is the most versatile pregnancy calculator around. It will instantly calculate gestational age or due date from any other reference point in the pregnancy. This app calculates exactly 280 days (40 weeks) from the first day of a woman's last menstrual period (LMP) and the estimated due date (EDD), and accordingly for any date in between. It automatically adjusts for leap year if needed.

Please note that the circular physical pregnancy wheels used are inherently inaccurate. Different pregnancy wheels may vary by as much as 3 or 4 days. Please keep this in mind when comparing the values obtained here to those given in clinics/hospitals.

Key Features


Use the icon to share your calculation as a link.

Responsive Web Design!

Visit the page on different browsers or screen sizes and the layout will rearrange itsolf for optimal interaction.

Calculate dates of pregnancy (from and to)

See the Changelog for a chronology of the features.

How to Use

Detailed Instructions

Date selection method:

Everything you see is a button! Touch any of the row labels or text output areas to bring up a date selection dialog box. You can calculate the dates and the gestational age using any date along the pregnancy as a reference point. For example, selecting EDD will allow you to enter an Estimated Due Date, and the app will calculate the rest of the dates according to the date you entered. Selecting Conception will allow you to enter a date for the approximate date of conception, and the other dates will be calculated relative to this date. The calculated data will appear in the light blue text boxes in the right hand column. You can also touch/click & along the boxes to smoothly scroll through the dates. Try it out! Abbreviations: LMP = Last Menstrual Period (use first day of period); EGA = Estimated Gestational Age; EDD = Estimated Due Date

Calendar Date picker:

Touch/click any square to select that date. The double arrow buttons change the year, and the single arrow buttons change the month. Touch/click cancel or anywhere outside the floating calendar to cancel. The center button will set the date to today.

Estimated Gestational Age (EGA):

To enter weeks and days for the gestational age, touch the "EGA" label or the text box to its right. The dates will be calculated accordingly.


This is the feature that sets this app apart from all others! It answers the questions: "What would the gestational age be at xxxx date?" and "When will the patient be at xx weeks gestational age?" Touch the "TimeMachine" text to set the date; this will give the gestational age for any given date. Touch the right side to input the gestational age, and it will calculate the date accordingly. Using TimeMachine does not affect any of the other rows or the base data.

Ultrasound dating:

The buttons at the top of the app will toggle the display of the alternate calculation methods including Ultrasound gestational age, IVF embryo implantation date, and Crown-Rump Length calculations. The ultrasound option is useful if you know what the gestational age was on a specific date (eg, ultrasound examination date). Enter the information as desired, and the app will calculate the dates accordingly. The information line at the bottom of the tab will also update to show ACOG's recommendations on when to use the ultrasound gestational age instead of LMP.

In-vitro fertilization (IVF) dating:

The IVF panel allows gestational age calcuation based on embryo age (days) and implantation date.

Crown-Rump Lenth (CRL) calculator

The CRL panel calculates the gestational age estimate based on crown-rump length measurement of a first trimester embryo. There is not one "standard" formula, so the calculator displays results based on a number of formulas. Each of the calculated gestational ages can be used as a point of calculation. Here are the formulas and referenced articles: