from what point can you accelerate up to 80km/h?

You can legally accelerate up to 80 km/h as soon as you can see the 80 km/h speed-limit sign , not only after you pass it, unless your local driving rules or exam question state otherwise.

Why “as soon as you can see the sign”?

Most theory and practice questions framed like:
“From what point can you accelerate up to 80 km/h?” with options such as:

• After you’ve passed the sign
• Two seconds before reaching the sign
• As soon as you can see the sign
• Immediately to match the signed speed

are designed so that the correct answer is: “As soon as you can see the sign.”

The idea is that the sign applies to the section of road starting at the sign, and you are allowed to be at that speed when you reach it, which means you may start accelerating in advance so that you are doing 80 km/h at or just after the sign, provided you stay within the previous limit up to that point.

Practical interpretation

In real driving:

• You keep to the current (lower) limit up to the area just before the new sign.
• You begin accelerating so that you smoothly reach about 80 km/h at the sign or very shortly after.
• You must still adapt to visibility, traffic, and conditions; if it is not safe to reach 80 km/h immediately, you accelerate more gently and only reach 80 km/h when safe.

Example to picture it

Imagine you are on a 60 km/h road and see an upcoming 80 km/h sign 150 m ahead:

• You remain at 60 km/h until you are near the sign.
• Over the last stretch before the sign, you gradually increase your speed so that, by the time your front bumper passes the sign, you are close to 80 km/h, without overshooting the old 60 km/h limit early.

TL;DR: In typical driving-theory style questions, you may accelerate to 80 km/h as soon as you can see the 80 km/h sign , so that you are at that speed by the time you reach it, as long as you still respect the previous limit and conditions.

Information gathered from public forums or data available on the internet and portrayed here.