# Calculate the simple flat interest rate on the invested amount (principal, initial starting amount of money lent, deposited or borrowed), of 100,000 units (Dollar, Euro, Pound, etc.), in order to produce an interest of 105,000 units, from date: Apr 30, 270, to date: May 28, 2035, namely for a period of 644,681 days (21,181 Months without 2 Days), if the commission fee (withdrawal) is 0%.

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## How to calculate / negociate the simple flat interest rate of a principal - initial starting amount of money lent, deposited or borrowed, in order to collect or pay a certain simple flat rate interest by the duration and any additional transaction fees (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 simple flat interest rate on the principal amount in order to earn a certain simple flat rate interest:

• 1) What is the simple flat interest rate of the principal S = 20,000 units 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?
p% = I ÷ (S × n) = 3,500 ÷ (20,000 × 5) = 3,500 ÷ 100,000 = 3.5 ÷ 100 = 3.5%
• 2) What is the simple flat interest rate of a principal S = 5,000 units, 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?
p% = I ÷ (S × n) = 300 ÷ (5,000 × 3) = 300 ÷ 15,000 = 3 ÷ 150 = 1 ÷ 50 = 2 ÷ 100 = 2%

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

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

### Formula of the simple flat interest rate of the principal for an annual simple flat rate interest calculated for a period of m months:

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

### Formula of the simple flat interest rate of a principal for an annual simple flat rate interest calculated for a period of d days:

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

### More examples of how the simple flat interest rate of a principal for a simple flat rate interest formula works:

• 1) Calculate the simple flat interest rate of the initial amount S = 400 units that would generate a simple flat rate interest I = 6.67 units in m = 5 months.