The hard part is asking
Most designers can do the maths. What they can't do is ask: they worry about sounding pushy or losing the next job. In practice, a late payment is often just forgotten, or stuck with someone in the client's accounts team. A clear, polite message with the exact amount and how to pay usually sorts it out.
These messages are the ones I use for my own clients, and they are the same ones Leostu copies for you from an order. Each one includes the project name, the amount due now, the invoice link and access code if you have them, and what happens next.
What to say at each stage
Deposit: the point is "work starts when the deposit arrives". The polite version attaches the contract and invoice and states the percentage and amount. The direct version says plainly that the work can't be scheduled until the deposit is in.
Balance: the point is "it's delivered, please arrange payment". The polite version confirms delivery, then mentions the balance. The direct version states how many days ago you delivered and the agreed due date, and that you will send the source files once paid.
Thank you: once you are paid in full, say thanks. Many people skip it, yet it is the cheapest way to open the next project.
When to use the direct tone
My habit: say nothing about money for three days after delivery. Days three to seven, send the polite version. Past the agreed due date, or two weeks after delivery with no reply, send the direct one. Direct is not rude. It simply lays out the facts: when you delivered, what is owed and when it was due.
After that, pick up the phone; it works far better than text. If your contract transfers copyright only after full payment, it is fair to remind the client of that clause, calmly.
Whatever the tone, keep it about the invoice, not about the person. "The balance of RM 6,360 was due on 20 October" is easier to act on than "you still haven't paid me", and it leaves the door open for the next project. Clients who feel accused tend to go quiet; clients who are given a clear amount and a clear way to pay usually just pay.
Keep a record
Send reminders in writing, even if you also call. A short trail of dated messages, each with the amount and the invoice, is what you will want if the project ever ends in a dispute. It also helps you: when a client says "I thought we paid that", you can point to the date the balance was requested.
Note what the client says in reply. "Finance pays on the 25th" is useful information; put it in your calendar and follow up on the 26th, not the 40th. "We are waiting for approval from the boss" usually means you should ask who the boss is and whether you can send the invoice to them directly.
Finally, be consistent. If you always send the polite version on day three and the direct one after the due date, clients learn your rhythm and many start paying before the first reminder.
Make it easy to pay
Include the invoice link and payment details so the client never has to ask where to send the money. Write the exact amount instead of "the rest" or "the balance". If the client has an accounts team, ask them to forward it.
If you use Leostu, delivered orders show up as "Balance due" on the dashboard and one click copies a reminder with the link and access code; the client sees an invoice with your payment methods. The button below carries the project and amount you entered here into a new order.