Work needed at once displaces other work and often means late nights. A rush fee is a fair way to cover that. It is not a punishment; it is an honest price for a changed schedule.
When to charge
Decide your normal turnaround, for example five working days. Anything faster than that is a rush. Say so in your first reply.
How much
Choose a percentage that reflects what you give up, such as a quarter on top of the base price for a short deadline, more for the same day. The calculator has a rush box for it.
An example
A shop asks for a festival video on Tuesday for use on Thursday. Normally the creator needs five days. She tells the shop the normal time, offers delivery on Thursday morning with a rush fee, and explains that the fee pays for moving other work. The shop chooses a simpler video instead, delivered on time, which saves both sides. A clear fee often leads to a better plan than a silent yes.
How to say it
"I can deliver by Friday. The usual time is five days, so there is a rush fee of ____ per cent." Clear, friendly and fair. If the deadline is impossible, say no.