This is probably the number one question asked around here and the good news is there is a VERY simple solution. The processes is also similar with the remaining platforms such as Booking.com Flipkey and Tripadvisor. 

Follow the instructions below. Set it and forget it! 

AIRBNB

Calendar importing

Calendar importing allows you to automatically keep your Airbnb calendar up to date with an external calendar that supports the iCalendar format, including Google calendar or the calendar on HomeAway or VRBO.

To import a calendar:

1. On airbnb.com go to Host and select Calendar
2. Click Availability settings in your calendar view
3. Under Sync calendars, select Import Calendar
4. Copy the URL for your other calendar into the Calendar address (URL) field
5. Name your calendar
6. Click Import calendar

If you edit an external calendar that syncs with your calendar on Airbnb, it will take a few hours for those changes to be visible to guests viewing your listing.

Calendar exporting

Calendar exporting lets you view your Airbnb calendar on an external calendar that supports the iCal format. To export your calendar in iCal format and add it to your external calendar:

1. On airbnb.com go to Host and select Calendar
2. Click Availability settings in your calendar view
3. Under Sync calendars, select Export Calendar
4. Copy and paste the Airbnb calendar link into your iCal applications

VRBO/HOMEAWAY

To import a calendar
Every property has its own reservation calendar, so select the one you want to affect. You can import up to five calendars. Events are kept up to date automatically.

1. In your reservation calendar, click the Import/Export arrows icon
2. Click Import Calendar
3. Give the calendar a name
4. Select a color to represent the calendar
5. In the URL field, paste the calendar address.
6. Change webcal:// to http:// in the URL
7. Select whether the calendar will block availability
8. Click Import Calendar

To remove a calendar

1. In your reservations calendar, click the Import/Export arrows icon
2. Click the name of the calendar
3. Click Remove and then confirm

To export your reservation calendar

1. In your reservation calendar, click the Import/Export arrows icon
2. Click Export Calendar
3. Copy the URL and follow the instructions on your external calendar in order to import