When will the world actually end?

The answer ultimately is determined by the sun. Most estimates are that the sun is halfway through its productive solar life so around five billion to seven billion years from now the sun will enter its red giant phase which will cause the sun to expand as the sun uses up the last remaining hydrogen in the sun's shell. This expanse will engulf Mercury, Venus and possibly Earth.

But that's billions of years in the future. Around 500 million years from now the sun's increased luminosity will make life on Earth extremely difficult if not impossible.