Calculates the future value of a single amount. Use the "future value schedule" if you want to calculate the future value of a series of investments or deposits.
Enter the present value (amount invested) and a nominal annual interest rate.
Date Math: If you change either date, the number of days will be calculated. If you enter a positive number of days, the end date will be updated. If you enter a negative number of days the start date will be updated.
The above means you can calculate the FV for a specific number of days and not worry about what the dates are. If you need to know the FV after 31 days, then enter 31 for the number of days and don't worry about the dates.
Set the compounding and the days per year. Click "Calc". The future value is calculated (initial amount plus the gain).
The gain may be calculated based on a unit of time, say a month. In that case, a month's gain is always the same for the same annual rate and same principal balance regardless of the length of the month. Given $10,000 principal and an annual rate of 6.75% the gain will be the same for February as it will be March.
Pick the date format you want to use by clicking on the "$ : MM/DD/YYYY" in the lower right corner of any calculator. You'll have 3 formatting options.
You may set a date by clicking on the calendar button  or by typing 8 digits per the selected date format.
If you are using the calendar, to quickly change to a new date, you may click on the current month's name at the top to see a list of months and then you may click on the year to see a list of years. Pick the year. Pick the month. Finally pick the date. Or click on the word "Today" to set to the current date.
If you are using the keyboard. Type only the 8 required digits. Do not type the date part separators ("/" or "-"). When you either tab to a date input or single click on a date, it will be selected. You can just start typing to clear. No need to delete the date. Or you can type the right arrow key to clear the selection and backspace to edit. Depending on the date format selected, you can backspace to clear the last 2 digits of a year and reenter them to change dates by multiple years very quickly.