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

https://www.slideserve.com/aaron_ward92/why-does-chatgpt-plus-cost-more-on-android-than-on-the-web

ChatGPT Plus is listed at $20 per month, but the actual price you pay can vary between about $13 and $27. This difference comes from extra fees like VAT or GST and app store markups on iOS and Android