ChatGPT Plus is listed at $20 per month, but the actual price you pay can range...

https://wiki-planet.win/index.php/Why_Do_My_Answers_Get_Worse_After_I_Hit_a_Limit_on_ChatGPT_Plus%3F

ChatGPT Plus is listed at $20 per month, but the actual price you pay can range from about $13 to $27. This happens because of extra taxes like VAT or GST depending on where you live, and app stores like Apple’s or Google’s add their own fees