When exactly is the Sun going to begin to inflate to become a Red Giant

I realize that it's not possible to be absolutely ecxact since the Sun is subject to Phases of varing energy output but the point is the sources on the Web vary between ONE Billion years and SEVEN Billion years. Is the margin of uncertainty really that big ? It must be possible to narrow down the end of Hydrogen more precisly.

I've always worked with about 4.5 billion years; it's based on how long the sun has been burning, what it's mass is, and how quickly mass in the sun is being converted to helium. I think the math works out to be between 4.0 and 5.2 billion years, and 4.5 was just a nice, middle-of-the-road number, because you're dealing with estimates of age, estimates of power output, and estimates of mass.

4 1/2 billion is the most commonly quoted number that I have seen.

What's the difference anyway? Neither you nor I will be around, and it is quite possible that there will not be any humans left by then, anyway

The current thinking is about 5 billion years.

The paper linked below presents some of the evidence for this.

it's estimated about 5 billion yrs , when it becomes a Red giant, after which it will proceed towards its end of life to become a white dwarf.

the sun is a myth and does not exist