A free trial becomes a paid subscription on the date in the confirmation email, not when you get bored of the app. The usual miss is Apple: you delete the app and the trial still converts in Settings.
Where trials hide
Search Gmail or Outlook for trial, free period, and renews on. Sort by date. The useful line is the end date, not the marketing subject.
Then open iPhone Settings, your name, Subscriptions. Trials billed through Apple sit next to Music and iCloud+. Web signup trials (Netflix, Spotify, ChatGPT in a browser) will not be on that list. Cancel those on the merchant site. Guides: Apple, Netflix, Spotify, ChatGPT Plus.
Statement check
A $0.00 or $1.00 authorization can appear before the real price. If the merchant name repeats a month later at full price, the trial converted. Upload 90 days in Unwanted Subscription if you do not want to hunt by hand. How to read a statement.
Cancel in the same sitting
Do not “decide next week.” Open the cancel page, confirm, save the email. If both Apple and the website could bill you, cancel both. That double-bill is how people pay for a trial they thought they killed.
The Unwanted Subscription scan is built for this pass: receipts, then a keep-or-cancel list, then a reminder if you keep something through the paid month.