That would work, but you also need to divide the interest rate by 2. That is, each year, the value increases by the factor (1+I/2)(1+I/2) instead of by the factor (1+I). Note that (1+I/2)(1+I/2) = 1 + I + (I/2)^2 and so you could also just change I to I+(I/2)^2 and keep the number of periods the same
– Dilip SarwateApr 11 '14 at 04:31
And having no power to change your great comment to an answer, I'll just suggest it here. It's 90% of the way there, just add tiny bit more. Your decision.
– JTP - Apologise to MonicaApr 11 '14 at 17:19