Small claims interest calculation

What is the name of your state? Ohio

I am getting ready to file in small claims court against a former customer who owes me about $1200.00 in unpaid tuition at my dance school. The form states that I can charge interest - How do I know what to charge, or did I have to have a late-payment interest policy in place before this occured? (I do have a $10.00 per month late payment fee that I did not include in the above amount.) Thanks for any help.

"The form states that I can charge interest - How do I know what to charge, or did I have to have a late-payment interest policy in place before this occured?"
*** In your claim, simply ask for 'statutory pre-judgment and post-judgment interest'.

"I do have a $10.00 per month late payment fee that I did not include in the above amount"
*** Include the contracted late fees in your total amount. Then, explain the claim at the hearing.

"Thanks for any help."
*** You're welcome.