Easy answer: Like
@foxbat says, two steps (at least). I also use the calculator Foxbat uses (the downloadable Excel spreadsheet version) 'cos it seems more versatile with a few more parameters that might help guide your choice (if they are valid parameters!). Note that "Brewunited" and "Homebrew Dad" are the same thing.
I use a minimum of two steps, not because I'm brewing high strength but because I brew twice the usual volume (45 litres, maybe 65).
Complicated answer: I'm just going through the trauma of trying to make these calculators work for me. Sometimes they do, sometimes they don't! Different calculators will return different results; because they all make their own assumptions based on observed evidence plus a large dollop of
guessing. I think most of the calculators work okay with yeast packs manufactured a month, maybe two, ago. After that, well the calculators keep putting out predictions and the packs appear to be within BBE dates, but in reality it's all stepped through the looking glass.
The calculators all attempt to predict
viability, which is probably the most important yeast parameter. Viability, or cell count comes close, is something you can have a stab at calculating. But another very important parameter is
vitality. How capable and "alive" (how much "get up and go") the yeast is and not just how much and can it stay alive. And you probably can't calculate this attribute.
As a yeast pack gets older vitality becomes more and more important. The notorious "Ringwood Ale" yeast (WYeast) often fails for people before it's three months old, yet some other yeasts go off like a bomb even when six months old.
I'm currently working with multiple steps (3 or 4) for older and notorious yeasts (starting with very small starters of 20ml or so, and only stepping up 3x volume each step or very much less). I used to give fewer steps more time (days) to get going but had it pointed out that this may not be a good approach.