The Excel FVSchedule function calculates the Future Value of an investment with a variable interest rate.
The syntax of the function is:
where the arguments are as follows:
principal    The present value of the investment. 
schedule   
An array of values that provides the schedule of interest rates to be applied to the principal. If provided as a range of cells, these may contain numeric values or be empty (empty cells denote a zero interest rate). 
In cell B1 of the spreadsheet below, the Excel Fvschedule function is used to calculate the future value of an investment of $10,000, over 5 years. The investment earns interest of 5% during the first two years and 3.5% during the 3rd, 4th and 5th years.
Formula:

Result:

For further details and examples of the Excel Fvschedule function, see the Microsoft Office website.
If you get an error from the Excel Fvschedule Function, this is likely to be the #VALUE! error:
#VALUE!   
Occurs if any of the supplied arguments are nonnumeric. (Although blank cells as a part of the schedule array are acceptable and are treated as the numeric value 0). 