Sneaker Bunko apologized in their official website that the information published on Monthly Shonen Ace and Young Ace magazines about the premiere schedule of Steins;Gate movie was wrong. The release date has not been fixed yet.

Source: Sneaker Bunko official website

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According to Monthly Shonen Ace magazine, Steins;Gate Movie was announced to be premiered this autumn. Shikura Chiyomaru, the original author of Steins;Gate game, revealed last September that the movie will not be a recap.

Sources: Scan of Shonen Ace, Chiyomaru's twitcast

List of the upcoming anime movies
Blood-C: The Last Dark (Jun 2nd)
Toshokan Sensou: Kakumei no Tsubasa (Jun 16th)
Berserk Ougon Jidaihen II: Doldrey Kouryaku (Jun 23rd)
Rurouni Kenshin: Shin Kyoto Hen Part 2 (Jun 23rd)
Mahou Shoujo Lyrical Nanoha: The Movie 2nd A's (Jul 14th)
Pokemon Best Wishes!: Kyurem vs. Seikenshi (Jul 14th)
Ookami Kodomo no Ame to Yuki (Jul 21st)
Naruto: Shippuuden Movie 6 - Road to Ninja (Jul 28th)
Code Geass Gaiden: Boukoku no Akito (Aug 4th)
Fairy Tail Movie: Houou no Miko (Aug 18th)
Tiger & Bunny Movie 1: The Beginning (September)
Fuse Teppou Musume no Torimonochou (October)
Evangelion: 3.0 You Can (Not) Redo (Autumn)
Mahou Shoujo Madoka★Magica Movie 1 & 2 (Autumn)
009 Re:Cyborg (Autumn)
Steins;Gate Movie (Autumn)
Gothicmade: Hana no Utame (Nov 1st)
One Piece Film Z (Dec 15th)
Berserk Ougon Jidaihen III: Kourin (Winter)