The Black Belt Personal Finance (BBPF) Bond Sensitivity Calculator allows the user to play "what-if" scenarios for anticipated changes in interest rates. In the economy the Federal Reserve changes interest rates depending on the state of the economy to stimulate or cool it down. When interest rates go up or down the value of bonds and bond funds change (e.g. when interest rates go up the value of the bond goes down). The app allows you to enter the value of your bond fund and several other parameters along with the anticipated change in interest rate and then model what the impact will be on the value of your bond or bond fund.
Note/Caveat: This app is meant to provide a quick and dirty back of the napkin analysis. You should consult with your financial advisor or accountant for a complete analysis.