I have recently seen some posts asking about the requirements to reach a new trust level but no real answer was given. (NB: These are estimates from sources available to me and may be incorrect)
TL0 (New User): Register on the forums
TL1 (Basic User): Read 5 topics, read 30 posts and have a read time of 30 minutes
TL2 (Member): Visit for 30 days (does NOT need to be in a row), like something, receive a like from someone, reply to 3 different topics, enter at least 20 topics, read at least 100 posts and have a read time of 1 hour (60 minutes)
TL3 (Regular) In the last 90 days you must have logged in 67% of those days, replied to at least 10 topics, must have viewed 500 topics, must have read 20000 of posts created in the last 90 days, must have received 60 likes (From 15 unique users over 20 unique days) and sent 30 likes, most not have been flagged more than 2 times, most not have been suspended. (Don’t forget you can lose TL4 by not meeting these standards)
TL4 (Leader) Leader can only be obtained by manual promotion.
Sources: https://meta.discourse.org/t/what-do-user-trust-levels-do/4924/30, what I have noted and help from other users! (Thank you!)
(The article notes the default values to reach new trust levels, I know that you need 30 days to go from TL1 to TL2 on this forum, but confirmation will be needed for the other values)
I apologise if this is a duplicate but I could not find anything like this after searching, I only found people asking and that is the reason this topic was created. I hope I helped.