minimum payment payoff calc

Hi everyone!

I am trying to build a calculator that will let me see how long it will take me to pay off a credit card if I just make minimum payments.

I've uploaded what i have so far and, compared to the results in the comparison tab (which were confirmed via two separate online calcs), my payoff is way off....years off in fact. What kills me is that my calcs are dead on until you get to month 8 and then it seems to go off the rails from there...

I feel like I am THIS close to mirroring those results....I just can't put my finger on it.

Any and all help is appreciated!
Respectfully yours,
Jonathan