A fixed deposit calculator is a tool used to calculate the amount of interest earned on a fixed deposit investment. To use the calculator, you will need to input the following information:

1. The amount of the initial deposit
2. The interest rate offered by the bank or financial institution
3. The duration of the fixed deposit investment

The calculator will then provide you with the following information:

1. The maturity value of the fixed deposit investment
2. The total interest earned on the investment
3. The monthly interest earned (if applicable)

The formula for calculating the maturity value of a fixed deposit is:

Maturity Value = P x (1 + (r/n))^(n x t)

where: P = Principal amount r = Annual interest rate (as a decimal) n = Number of times the interest is compounded per year t = Time period of the investment in years

The formula for calculating the total interest earned on a fixed deposit is:

Total Interest = Maturity Value – Principal Amount

The formula for calculating the monthly interest earned on a fixed deposit is:

Monthly Interest = (Total Interest / Number of Months in Investment)