Investment Calculator
Initial ($), Monthly add ($), Annual return (%), and Years project a future value for a lump sum plus a monthly contribution. The annual rate is divided by 12 and the term is counted in months.
How to use
- Put the starting balance in Initial ($). The sample is 10000. Use 0 if you are only testing the monthly deposits.
- Put the amount added each month in Monthly add ($). The sample is 200. Use 0 for a lump sum with no new money.
- Type a yearly percent in Annual return (%), such as 7, not 7 divided by 12. The script divides by 100 and then by 12.
- Type Years. The script multiplies by 12 to get the number of months.
- Click Calculate. The large figure is the future value. The line under it is Total contributed and Growth.
When it helps
Use it to sketch a savings plan where the same dollar amount goes in every month and the yearly return stays flat. Growth is the future value minus everything you put in, so you can see how much of the ending number came from deposits rather than from the rate.
A lump sum with no monthly add, and a choice of compounding other than monthly, belongs on the compound interest calculator. To see what the ending dollars might buy after a constant rise in prices, run the same horizon on the inflation calculator. This page does not inflate the result for you.
Limits
Compounding is monthly only. Fees, taxes, and a varying return are not on the form, so the result is arithmetic on a fixed rate, not a brokerage quote and not a lender quote. A zero Annual return (%) skips the power formula and adds Initial ($) to Monthly add ($) times the number of months.
Deposits follow an end-of-month pattern: a contribution does not earn a return in the month it is added. Future value, Total contributed, and Growth are rounded to whole dollars, so each can sit under a cent-level sheet by less than a dollar. The page will not model a raise, a skipped month, or a rate that changes after year five.
Questions
Where does the monthly rate come from?
Annual return (%) is turned into a decimal, then divided by 12. Years becomes months by multiplying by 12. The future value is the grown lump sum plus the grown stream of monthly adds. That is the whole model.
Does Growth include my deposits?
No. Total contributed is Initial ($) plus Monthly add ($) times the month count. Growth is future value minus that sum. If the rate is zero, Growth is zero.
Can I type a fee or a tax drag?
No. There is no expense field and no tax field. Lower Annual return (%) yourself if you want a rough haircut, and treat the output as arithmetic rather than a fund statement.