If you have a savings account or other investment with compound interest, then you gain a percentage of money from both your original deposit and all accrued interest. Over time, an account with compound interest will increase faster than one with simple interest. To calculate compound interest for 30 years, you use the formula P(1 + i)^n.
Write down the amount of your initial investment and the interest rate of your account.
Convert the interest rate of the account into a decimal and add 1 to it. For example, if your account has a 5 percent interest rate, then you would add .05 to 1 to get 1.05.
Put the result from Step 2 to the power of 30, since that is the number of years you are calculating compound interest for. For example, if your result from Step 2 is 1.05, then put 1.05 to the 30th power to get approximately 4.32.
Multiply the result from Step 3 by the amount of your initial investment to find the balance of your account after 30 years of compounded interest. For example, if your result from Step 3 is approximately 4.32 and you originally invested $1,000, then you multiply 4.32 by $1,000 to get $4,320.
Bennett Gavrish is an I.T. professional who has been writing about computers, electronics and the Web since 2004. His work has appeared in the "Nashua Telegraph" and the "Daily Free Press" and on numerous websites. Gavrish received a bachelor's degree in journalism from Boston University.