I know the below formulas to calculate Gains/Losses IF you have auto-reinvest in mutual funds.

Gain or Loss = Sale Price - Cost Basis
Cost Basis = {Original Cost Purchase + (Sum of all Capital Gains + Dividends)}

How about individual stocks? Do the above formulas still apply?

For example. I have a stock that pays $100 per quarter in dividends. If I use that $100 and buy more shares of the same stock, how does this affect my cost basis?

Thanks