The listed ChatGPT Plus price is $20 per month, but the actual charge can vary...

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

The listed ChatGPT Plus price is $20 per month, but the actual charge can vary from about $13 to $27 depending on where you subscribe. This happens because taxes like VAT or GST and extra fees added by app stores affect the final cost