Conflicting numbers from different calculators; which one is right?

[DavetheDog]

I just smacked my Wyeast 1388 Belgian Strong Ale and am now planning for the starter later this afternoon. I'm brewing the Belgian Strong Golden Ale from NB. Typically, I use Beersmith 2 but have been digging around as I sometimes question Beersmith's numbers. Can you guys have a look at the numbers below and give me some feedback please. Let me know if you need more info and as always, thanks for the input.

Recipe:
OG: 1.080
Batch Size: 5.25 gal
Type: extract
Yeast: Wyeast 1388 Belgian Strong Ale (manufactured 2/28/2013)
Stir plate: Yes

Beersmith:
Yeast Cells Needed: 273.7 Billion
Starter Size: 1.2 liters
Yield: 273.7 Billion
Yeast Viability: 96%

Mr. Malty
Yeast Cells Needed: 287 Billion
Starter Size: 2.57 liters
Yield: info not given
Yeast Viability: 71%

As you can see the starter sizes are quite different as are the needed cell count and viability. Who is correct?

Beersmith 2 seems to be the leading software but as mentioned, I sometimes a question the numbers. How accurate is it?

 

[winvarin]

Check your viability numbers. Beersmith looks to be giving you the starter volume based on 96% viability. Mr Malty is going off 71%.

In mr malty, there is a viability calculator when you input the date. Wyeast uses a packaged date if memory serves. Input that date into the calculator and it will make the viability calculation and suggest your starter size from there

If you use a white labs yeast, they give a "best by" date, which is, and someone here correct me if I am wrong, 4 months after the package date. So if you use white labs, subtract 4 months from the date on the vial and use that in the calculator

 

[jflongo]

I just did YeastCalc as well.

2L starter @ 1080 OG @ 83% viability

Says you will end up with 364 billion with a stir plate.
Says you will end up with 235 billion by shaking it from time to time.

Are you using a stir plate? If I were you, I would go with the 2L on a stir plate if you have one, that should be fine.

 

[winvarin]

And by viability, they mean the viability of the yeast you are putting in your starter, not the viability of the yeast after your starter grows

 

[jflongo]

And by viability, they mean the viability of the yeast you are putting in your starter, not the viability of the yeast after your starter grows

I have noticed yeastcalc drops it by ~10% / month of the manu date.

So 71% seems low to me and 96% way to high. I would go with YeastCalc around 83%.