Do you have to double the big blind after the turn?

That was the search term in a google search that landed someone on this blog recently. I doubt that they found the answer to the question her, but I'll try to answer it now.

In no limit poker the minimim bet at each betting round is usually the amount of the big blind. It does not increase on the turn.

But --- some online sites do have software that changes the minimum to twice the big blind on the turn. That happens because they based their software design on an initial design for limit games, not because of a general poker rule.

In some poker rooms a straddle might complicate things somewhat. Depending on local rules the minimum bet might be the amount of the straddle at each round, or it might be the amount of the straddle preflop then the amount of the big blind thereafter. But the minimum won't double on the turn.