# Calculator: calculate the amount of initial money to be lent, deposited or borrowed (principal) in order to earn a simple flat rate due interest by the interest rate, duration and additional transaction fees (withdrawal, payment in advance)

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## How to calculate the principal - initial amount of money lent, deposited or borrowed in order to collect or pay a simple flat rate due interest by the interest rate, duration and additional fees (transaction fee as withdrawal, payment in advance, etc.).

• #### I = S × p% × n

• I = n years simple interest charged
• S = initial amount (principal)
• p% = annual simple flat interest rate (percentage of the principal charged as interest)
• n = number of years of the lending or borrowing the money

### Examples of how to calculate the initial amount, the principal, to earn a certain simple flat rate interest:

• 1) What is the principal that has to be lent, deposited or borrowed for a period of n = 5 years if the simple flat rate interest collected or paid D = 3,500 units, for an annual simple flat interest rate (percentage) p% = 3.5%?
S = I ÷ (p% × n) = 3,500 ÷ (3.5% × 5) = 3,500 ÷ (3.5/100 × 5) = (3,500 × 100) ÷ (3.5 × 5) = 350,000 ÷ 17.5 = 20,000 units
• 2) What is the principal that has to be lent, deposited or borrowed for a period of n = 3 years if the simple flat rate interest collected or paid D = 300 units, for an annual simple flat interest rate p% = 2%?
S = I ÷ (p% × n) = 300 ÷ (2% × 3) = 300 ÷ (2/100 × 3) = (300 × 100) ÷ (2 × 3) = 30,000 ÷ 6 = 5,000 units

### Annual simple flat rate interest formula calculated for a period of n years:

• Principal, S = I ÷ (p% × n)
• Simple interest, I = S × p% × n
• Simple flat interest rate, p% = I ÷ (S × n)
• Number of years for the period of the deposit, lending or borrowing, n = I ÷ (S × p%)

### The principal formula for earning an annual simple flat rate interest calculated for a period of m months:

• Principal, S = (12 × I) ÷ (p% × m)
• Simple interest, I = (S × p% × m) ÷ 12
• Interest rate, p% = (12 × I) ÷ (S × m)
• Number of months of the period, m = (12 × I) ÷ (S × p%)

### The principal formula for earning an annual simple flat rate interest calculated for a period of d days:

• Principal, S = (365 × I) ÷ (p% × d)
• Simple interest, I = (S × p% × d) ÷ 365
• Simple interest rate, p% = (365 × I) ÷ (S × d)
• Number of days of the period, d = (365 × I) ÷ (S × p%)

### More examples of how to calculate the principal for earning a simple flat rate interest:

• 1) Calculate the initial amount S that would generate a simple flat rate interest I = 6.67 units in m = 5 months with a simple interest rate of p% = 4%.