Stupid invest vs. pay mortgage question

Came across this calculator on the internet:

http://ift.tt/1Bg35AU



If you type in loan interest rate = 6%, loan interest deductibility = no, long term investment return = 6%, investment type = tax deferred, and anything for the rest of the slots, shouldn't this give the result that investing vs. paying mortgage are equal?



For what I typed in, I get final loan balance = 2193595.54

Investments - loan balance = -2193595.54

And it says "In your case it is wiser to prepay than to invest."

So I thought, maybe this is just a break even thing where it says pre-pay is better when the answer is exactly the same. So I tried moving it by a tenth of a point, and the results don't seem to make sense. I'm wondering if this calculator is forgetting to put a negative sign on the loan balance when making the comparison?

After experimenting some more, the cut off seems to be

Invest if [Investments - loan balance] > loan balance

When shouldn't it be

Invest if [Investments - loan balance] > - loan balance



Or am I missing something....?



I feel like I must be missing something, because if you google invest vs. pay mortgage this calculator is on a billion websites doing the same thing.



hoping i'm just being dumb here

Stupid invest vs. pay mortgage question