How do I write a contract?

I'm trying to write a contract where my dad is aloud to borrow my cellphone for one week. $21 up front, or $2 a day with 50 cents for each call made or received. Also, a $10 safety deposit for scratches, if the call history has been tampered with, etc. and $50 if he loses it. Please help me write a contract with minimal loop holes. Thanks
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A contract requires an offer and an acceptance. It doesn't have to be perfect language necessarily, but the language should be clear enough that everyone understands it.

You would write:

I, John Smith, agree to pay my son, Jerry Smith, $21 for use of his cell phone for one week's period, starting on this date and ending on this date at this time. I also agree that I will pay $2 per day, and will be charged $.50 for every phone call that I place or receive. In addition to the $21 down payment, I have made a $10 refundable security deposit in case the phone is scratched. I will forfeit this deposit if the phone is lost or stolen, and will be charged an additional $50.

Then you basically state in the same type of language that you acknowledge that you have received the money from your dad. You both should sign and date the thing at the bottom.

Just a piece of advice, this contract is way too complicated. You should make it simple and just charge him a flat fee to borrow the phone for a week, and charge him for each additional day that he keeps it after a week. The deposit for scratches is ridiculous, because it will be hard to prove, and scratches on a cell phone are considered wear and tear. I agree that your father should be held responsible if the item is lost or stolen.

Also, why do you need a contract for this? Unless you will take your father to court over less than $100 (which isn't worth the filing fee), then I wouldn't bother having a contract at all.

-Matthew