This is a very relevant topic, Tim. I'd be happy to contribute to your research however I can.Late payments are a pain in the backside. It doesn't affect the business too much, but causes us stress. You wonder why they're not paying their invoice... are they unhappy, is there a problem? I suspect that clients sometimes deliberately delay payment of invoices pending a satisfactory outcome to the project, even if they have agreed to be billed monthly on account. The more they owe you, the more power they have over you because they know you'll have to bend over backwords to please them if you want the outstanding invoices paid. They like to "hedge their bets" even if that's not the payment terms they agreed to.We often have to chase payments, usually when there is a lazy finance department involved and they blame people moving roles and suchlike. One client we had took 270 days to settle a fairly large invoice!!! When they came to us for the next project, I quoted them a day rate of £3,000. I kid you not, I really did quote them that. When the inevitable "WTF" response came back to us, I said we had to charge more to cover the financial risks associated with working with them - a risk premium if you like. Eventually they settled on paying a deposit up-front.What I do now is raise the first invoice on day 1 of the project so that I get an early heads-up as to whether the client is going to be a tardy payer. They know the first invoice will be billed on day 1 so it's not a surprise to them. If I know a client is a late payer for whatever reason, I put our fees up. We can't afford to spend hours arm wrestling with useless accounts payable departments.