Then try this Retirement Planning Calculator. It solves for multiple unknowns and creates a cash flow schedule.
Check out our Internal Rate of Return (IRR) Calculator. It supports irregular investment dates.
Note: If you have multiple investments or witdrawals on different dates then use this internal rate of return calculator. An IRR calculation is an annualized ROI calculation when there are multiple cash flows.
Update 03/15/2016: Per below comments, a few changes have been made to make it easier (hopefully) to enter dates. As before, you can enter any date by typing 8 numbers or you can use a calendar. But now the two methods do not interfere with each other. The calendar will not display unless you click on the calendar button .
When using the calendar, click on the month at the top to list the months, then, if needed, click on the year at the top to list years. Click to pick a year, pick a month and pick a day. Naturally you can scroll through the months and days too. Or you can click on "Today" to quickly select the current date.
If you prefer not using a calendar, single click on a date or use the [Tab] key (or [Shift][Tab]) to select a date. Then, as mentioned, type 8 digits only - no need to type the date part separators. Also, because the date is selected, you do not need to clear the prior date before typing. If mm/dd/yyyy is selected for the date format, for March 15, 2016, type 03152016.
ROI or Return on Investment calculates the percentage gained or lost on an investment.
Enter the "Amount Invested" and the date the investment was made ("Start Date"). Enter the total "Amount Returned" and the end date.
You can change the dates by changing the number of days. Enter a negative number of days to adjust the "Start Date". Or as you change a date the "Number of Days" will update.
The results include the percentage gained or loss on the investment as well as the annualized gain or loss also expressed as a percent. The annualized return can be used to compare one investment with another investment.
Example: If you bought $25,000 worth of your favorite stock on January 2nd 2014 and sold it for $33,000 on June 7th 2015, you would have a gain of $8,000 which is 32%. The annualized gain is 21.5%.
Now, lets say you made a second investment on January 2nd, 2015. This time for $10,000 and you sold it for $11,000 on March 1st, 2015. The gain is only $1,000 or 10%. However, annualized the gain is 82.1%. Ignoring risk (which can be very dangerous), one would generally consider the latter investment to be better than the former.