N3 — outside your level filter
the reason is — stages the question the listener is about to ask, then answers it
今日は早めに帰るね。どうしてかというと、明日の朝がすごく早いからなんだ。
kyou wa hayame ni kaeru ne. doushite ka to iu to, ashita no asa ga sugoku hayai kara na n da.
I'm heading home early today. The reason being, I have a really early start tomorrow. casual
この方法をおすすめします。なぜかというと、失敗しても元に戻せるからです。
kono houhou o osusume shimasu. naze ka to iu to, shippai shite mo moto ni modoseru kara desu.
I recommend this method. The reason is that you can undo it if it goes wrong. neutral
Variants
どうしてかというとdoushitekatoiutocolloquial
the everyday spoken twin — explaining to a friend or a child; どうして is the softer question word, so this shape almost never appears in writing.
なぜかといえばnazekatoiebaliterary
the ば conditional in place of と — written argument and speeches, alongside なぜならば.
なぜかと言いますとnazekatoiimasutoformal
polite 言います in place of the plain 言う, for presentations and customer-facing explanation, where the bare と would sound clipped.
なぜかというと
なぜかというとnaze ka to iu toN3neutral