Where the movies fit in?
 

So I'm working through my first Kamen Rider series with W. Loving the show, just finished episode 34. I know there are some movies that feature W in them. Where do those fit in? Do I wait until I've finished the series to watch them, or are they made to be watched somewhere in the middle of the season?

Most movies in general i just watch after the series. Did that with kiva-ooo and i still need to see fourzes movie

W is one of the rare series where the movies are actually part of the plot. You should watch Begins Night around episode 13, A to Z around episode 45 (someone will doubtless correct me on the exact episodes), and Movie Ware Core, W Returns Accel, and W Returns Eternal after the series (and in that order).

Most movies will blatantly be advertised during the series, replacing the opening with clips from their respective movie.
That's a relatively decent indicator of when to watch them.

Here's your W movie timeline:
Begins Night (Part of Movie War 2010) is set between episodes 14 and 15.
Forever A to Z is set between episodes 44 and 45.
Eternal Returns is set after the end of the show.
Message from Skull (Part of Movie War Core) is set after the end of the show.
Accel Returns is set after Message from Skull.

Begins Night and A to Z are part of the show's plot. Begins Night resolves a sub plot while A to Z introduces a concept used in the finale.

Awesome, thanks a lot guys. This really helps me out. Good thing I asked before completing the series.

Is this trend of having movies fit in the middle of the season true for OOO and Fourze too?

For OOO, yes. Fourze's movie takes place after the series (However, Movie War Megamax does have some impact on Fourze, notably the S-1 switch).
However, OOO's movie isn't necessary to watch like Double's.

I disagree, between 16 & 17.

Not really. Aside from Mega Max, which takes place after the series, none of the OOO movies are canonical. Fourze's movies fit in as side stories, but none of them are as vital to the plot as W's.

Nay, it's suppose to be before he gets the Fang Memory. It's semantics eitherway as long as it's in the teens.