Do you have to pay monthly to play World of Warcraft?

Yes. A recurring subscription is what keeps your account playable past level 20, and it's been priced around $15 a month since launch, with discounts if you commit to a 3-, 6- or 12-month block. That single subscription is all you need — it unlocks both retail WoW and WoW Classic (including its current seasonal ruleset) on the same account, not two separate purchases.

The free trial only goes so far. Before you pay anything, you can create a character of any class and play it all the way to level 20, with no time limit — but you can't trade, use the mailbox or Auction House, join a guild, or use most chat channels. Reaching level 21 is what actually requires a subscription; the level cap, not a clock, is the wall.

You don't need to buy every expansion. Blizzard folds older expansions into the base subscription once a new one ships, so right now everything up through the last few expansions comes with your sub. What you do need to buy separately is the current expansion — today that's Midnight — because its new zones, instances and level cap are gated behind that purchase, not behind the subscription.

You can also pay with gold instead of cash. The WoW Token, sold in the in-game shop for around $20, can be listed on the Auction House for gold; whoever buys it with gold redeems it for 30 days of game time (or Battle.net Balance). It's Blizzard's official channel for turning wealth earned in-game into subscription time, without touching a real-money trading site.

So the honest total is: a subscription to play at all past the trial, and the latest expansion if you want its new content — nothing else is mandatory.