Charge for late payment

[koster]

If I want to charge someone interest for making a late payment, how should I calculate it? What is a standard rate?

[erimus1]

You can not do this unless it is written into the contract. Many companies do this the other wat around - they give a discount for early payment, but if it is paid after a certain date, then this discount is taken away. You can charge whatever price you want - it is a free economy.