The Max Cookies Upgrade increases the maximum amount of cookies that appear on screen by 3 for each level of upgrade.
You initialy start with 20 cookies maximum aloud on screen.
The maximum is 167 cookies on screen.
You can find out your current maximum of cookies with the formula:
M(n) = 20 + 3(n-1)
M(n) is the maximum amount of cookies you can have
n is the upgrade level of your Maxi Cookies
The initial cost is 4000 cookies and doubles in cost for each upgrade level.
It costs 2,251,799,813,685,248,000 cookies for the final level (50).