I’ve seen a few people write that we can’t update our calendar with dates when we are unavailable.
We can, I have.
So here goes. Hopefully I’ve got the steps correct if you want to try
Go to
Me
View and Edit Profile
Availability
Edit - This takes you to Dashboard
Scroll down to
My sitter Profile -under my 1st pic
Manage Availability
Enter dates and add
Hope this helps
@Newt The dates you add in under Manage Availability are those when you are available. The default calendar is set to being unavailable. I get a sense that you’re perhaps reading it in reverse. 
It doesn’t appear like that when I view my own calendar. It shows as a yellow block which would indicate to me not available rather than available. Obviously I can’t see what the HO will see.
@Newt, I would have to agree with the very knowledgeable Snowbird, who was a former Forum Moderator.
Everyday a school day
@Newt It’s not surprising that you thought it was the reverse as most find the calendar illogical. Add to that there’s no legend and it’s basically useless, other than to see confirmed TrustedHousesitters sits (black line across dates on white background).
Just to clarify the wording on the Manage Availability, I’ll add an image of it here. You’ll see the wording shows to add dates when you are available.
You are able to see what homeowners see when viewing your profile. On the website, search for a sitter for your home town. Then scroll through until you see your profile photo. If you click on that, you’ll see the version homeowners see. It’s always a good idea to check that, especially if you change content … or if TrustedHousesitters changes format, which they have done in the past without notifying members. 
Thanks @ziggy 
I’ve had a look, I see what you mean it looks like a very easy fix for THS to just show highlighted dates as unavailable. And to include a short cut to the edit cal
Calendar page, am I to assume that they have no intention/interest in doing so ?
No - we have been asking for years
Do you know if the calendar are accessible/visible to others if you are both HS and HO?
@biscuit I only have sitter membership so I don’t have any info on what homeowners can see or access. Hopefully someone with a combined membership can answer your question.
I suppose they could do a search for a sitter and view it, the same way I suggested earlier (post # 5 above).
Yes, we all see it as an easy fix, but it never gets sorted. That’s why a lot of sitters are like us whereby we just don’t bother completing it, because a home owner ‘could’ interpret the calendar the exact same way as you did at first glance, in a completely misleading way. Plus how you view it is different depending on whether you view it on a laptop or mobile, it’s silly, and so simple to fix.
Thank you 
I am pretty sure that HOs see what anybody can see.
But: there is this other problem with the interface that the calendar is not displayed on the preview of their own profile that most sitters use!
For that, one needs the other profile link, the one that is on one’s Dashboard, at the bottom. Or one needs to look up oneself among the sitters in one’s own town.
Yes, these are three issues with the web interface that should be trivially easy to fix but THS has left it this way since they got this software. Instead, they are tinkering with other stuff.
@Snowbird it looks the same
