計画 includes personal plan, schedule. あなたの明日の計画は何ですか？(OK) What is your tomorrow's plan? あなたの明日の企画は何ですか？(strange) It might be possible if there is a party or event tomorrow, and ask what kind of performance you are planning. But otherwise it is strange to use 企画. 企画 usually means projects, events. 企画 can not be used as a forecast of amount. この会社の来年の販売計画は？　What is the sales plan of this company next year? The answer may be "1.2 million in January, 1.4 million in February, 1.0 million in March...." この会社の来年の販売企画は？ What is the sales plan of this company next year? The answer may be "Special campaign on March, New advertisement on August.." I hope you can get some idea through these examples.

企画：計画を立てること。make a plan. 計画：プラン。plan.