Ok - my question is - how is 'uptime' calculated?

Like, when you sign up for a hosting plan and the host guarantees something like 99% uptime - how is the calculated?

i am wondering because my email is not working and in the past i have been down quite a bit - i would like to leave my host based on this and i think i should get a refund for my remaining months, based on the fact that i was promised a certain amount of uptime and it seems that i am not getting it.

Ask your host for a refund and let them know why you are leaving them.

Check their policy or TOS and see what the guarantee and what your compensation is for the downtime.