There is little if any difference. They both sound natural. The first is more common. "Decide for yourself" emphasizes independence. You may be talking to many people, but you not ask them what to do. You should make the decision. "Decide on your own" emphasizes isolation. You should look directly at information and data. You should make the decision without asking for anybody else's interpretation or advice.

In deciding something for yourself, you may talk to your parents, your friends, and respected elders to see what advice they have to offer. You can ask them what to do. However, in the end, it is YOU who must make the choice. You have to decide "for yourself". It means you make the decision that works for YOU. We use the reflexive pronoun "yourself" instead of "you".

You have to decide for yourself. Meaning: Make a decision based on personal preferences. Focus: Personal autonomy. You have to decide on your own. Meaning: Make a decision without outside help. Focus: Independence.

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