Because in Tagalog

Which one to use

Use kasi in everyday conversation: Hindi ako nakapunta kasi umuulan (I couldn't go because it was raining). Dahil works in both speech and writing, and dahil sa before a noun means "because of": Hindi ako dadalo dahil sa ulan (I won't attend because of the rain). Sapagkat is the formal word you will see in written and formal Tagalog. Start with kasi for conversation, and use dahil when you want a more neutral tone.