How can I calculate the interest earned on $400.00 in a regular savings account?

You need to know the interest rate of the account. You also need to know if the interest compounds continuously, quarterly, or annually. Savings accounts generally do not pay much. Let's assume a low rate of 1% to see the calculation and further assume that it compounds annually. Your actual amount may be different depending on these assumptions. The formula is given in the article above, Value = P(1+r/n)^(nt). P is the principal of $400. R is the rate, which we assume to be 0.01, and n is the number of times per year that it compounds, so n=1, and t=32, then number of years. Put these together : Value = 400*(1.01)^32 = 400*1.375 = $550.