Keep in mind that a handshake deal is just as legally binding as a contract written in stone, as long as it meets the three legal requirements for a contract: 1) offer, 2) acceptance, and 3) consideration.
The only real difference is that a verbal contract is a lot more difficult to prove, if challenged.
So really, you probably
are working under a contract, just not one on paper, as long as the client has offered you the gig, you've accepted it, and you both have agreed on the money. Again, it's just a lot harder to prove. At
that point (the point of hashing out the working agreement) you should mention that you will be adding late charges on outstanding balances for overdue invoices.
Mentioning it for the first time by noting it on a client's first invoice is, at least legally, useless. They might be nice enough to pay it anyway, or legally naïve enough not to question it... but either way they are under no legal obligation to do so. If you spell it out in advance, then they are.
T2
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Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com