When you have IRCv3 tags enabled you get extra data like this:
← @badges=moderator/1,subscriber/24,bits/10000;color=#FF4BD3;display-name=Matt_Thomas;emotes=;id=91b26539-469d-447e-a338-0079e44f5fce;mod=1;room-id=60343212;sent-ts=1493851243246;subscriber=1;tmi-sent-ts=1493851242665;turbo=0;user-id=35805066;user-type=mod :matt_thomas!matt_thomas@matt_thomas.tmi.twitch.tv PRIVMSG #schyax :derp
Looking at the breakdown by line:
badges=moderator/1,subscriber/24,bits/10000;
color=#FF4BD3;
display-name=Matt_Thomas;
emotes=;
id=91b26539-469d-447e-a338-0079e44f5fce;
mod=1;
room-id=60343212;
sent-ts=1493851243246;
subscriber=1;
tmi-sent-ts=1493851242665;
turbo=0;user-id=35805066;
user-type=mod
:matt_thomas!matt_thomas@matt_thomas.tmi.twitch.tv PRIVMSG #schyax :derp
You can see the badges area subscriber/24 - This means 24 months. The values will only be that of the sub badges but I think it might work for your needs.