Question: what is the formula for compound interest quarterly?
Answer: If interest is compounded yearly, then n = 1; if semi-annually, then n = 2; quarterly, then n = 4; monthly, then n = 12; weekly, then n = 52; daily, then n = 365; and so forth, regardless of the number of years involved. Also, "t" must be expressed in years, because interest rates are expressed that way.