When congratulating someone on graduation or signing a graduation card, we usually say or write "congratulations on your graduation".

When congratulating someone on graduation or signing a graduation card, we usually say or write "congratulations on your graduation".

Congratulations on your graduation, and best wishes for your next adventure.

More examples:

Congratulations on your big day!

Congratulations on this special achievement

In general, the noun "congratulations" is more commonly followed by "on"; for example, we typically say: "congratulations on your marriage", "congratulations on the birth of your baby", or "congratulations on your achievement".

Congratulations on the birth of your daughter.

When getting a new job or promotion, you can use the preposition "on" or "for" and say, for example, congratulations for/on your new job.