ChatGPT Plus has a listed price of $20, but the actual cost you pay can vary...

https://highstylife.com/i-keep-hitting-chatgpt-limits-should-i-start-a-new-thread/

ChatGPT Plus has a listed price of $20, but the actual cost you pay can vary from about $13 to $27. This difference happens because of taxes like VAT or GST and extra fees added by app stores on iOS and Android