You can add a calendar to Tumblr using Google Calendar. Adding a calendar can be very useful for a business website. It can add a booking feature, an events schedule or hours of operation. There are plenty of services out there that will charge you on average $19/month to give you a similar setup, but with Google Calendar you can do it for free. I won't show you how to set up a booking system in this tutorial, I will just show you how to install Google Calender on your Blog. If you would like to use the free Google Calendar for booking appointment scheduling type setup, click here.

Create a Google Calendar account

1. Go to https://www.google.com/calendar/ and create an account.
2. Set time zone.
3. Create Google Calendar events(s).

Get the Google Calendar embed code snippet

1. Log into your Google Calendar account if you're not already.
2. Click on the settings icon then select 'Settings' from the drop-down menu.
   
3. Select the 'Calendars' tab, then click the link title of your calendar.
   
4. Select and copy (Ctrl-c) the entire code snippet.
   

Paste the Google Calendar embed code into your Tumblr website

Embed video code manually

1. Log into your Tumblr account.
2. Follow these instructions on how to create a page in Tumblr and create a page called 'Events'.
3. Click on the 'Preferences' icon.
   
4. Click the 'Customize your blog' button.
   
5. Click on the page you want to edit, from the 'PAGES' area.
6. Click the 'HTML' icon from the menu.
   
7. Paste the Google Calendar embed code into the window.
8. Click the 'Save Page' button.

You've successfully added a calendar to Tumblr and it will be visible to the public when they view the page.