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# Python Program for compound interest

Let us discuss the formula for compound interest. The formula to calculate compound interest annually is given by:

A = P(1 + R/100) t

Compound Interest = A – P

Where,
A is amount
P is the principal amount
R is the rate and
T is the time span

Example:

Input: Principal (amount): 1200, Time: 2, Rate: 5.4
Output: Compound Interest = 133.099243

Example

## Python3

 `# Python3 program to find compound``# interest for given values.`` ` ` ` `def` `compound_interest(principal, rate, time):`` ` `    ``# Calculates compound interest``    ``Amount ``=` `principal ``*` `(``pow``((``1` `+` `rate ``/` `100``), time))``    ``CI ``=` `Amount ``-` `principal``    ``print``(``"Compound interest is"``, CI)`` ` ` ` `# Driver Code``compound_interest(``10000``, ``10.25``, ``5``)`

Output

```Compound interest is 6288.946267774416
```

Time Complexity: O(1) since no loop is used the algorithm takes up constant time to perform the operations
Auxiliary Space: O(1) since no extra array is used so the space taken by the algorithm is constant.

Method#2: Input taking from user.

In this method we are going to calculate the compound interest by taking input from the user by using above formula.

## Python3

 `# Python3 program to find compound``# interest for input taking from user.`` ` ` ` `def` `compound_interest(principal, rate, time):`` ` `    ``# Calculates compound interest``    ``Amount ``=` `principal ``*` `(``pow``((``1` `+` `rate ``/` `100``), time))``    ``CI ``=` `Amount ``-` `principal``    ``print``(``"Compound interest is"``, CI)`` ` ` ` `# Driver Code``#Taking input from user.``principal ``=` `int``(``input``(``"Enter the principal amount: "``))``rate ``=` `int``(``input``(``"Enter rate of interest: "``))``time ``=` `int``(``input``(``"Enter time in years: "` `))``#Function Call``compound_interest(principal,rate,time)`` ` `#This code is contributed by Vinay Pinjala.`

Input:

Enter the principal amount: 3000

Enter rate of interest: 5

Enter time in years: 3

Output:

Compound interest is 472.875

Time Complexity: O(1) since no loop is used the algorithm takes up constant time to perform the operations
Auxiliary Space: O(1) since no extra array is used so the space taken by the algorithm is constant.

Method #3:  Finding compound interest of given values without using pow() function.

## Python3

 `# Python code``# To find compound interest `` ` `# inputs ``p``=` `1200`   `# principal amount ``t``=` `2`      `# time ``r``=` `5.4`    `# rate ``# calculates the compound interest``a``=``p``*``(``1``+``(r``/``100``))``*``*``t  ``# formula for calculating amount ``ci``=``a``-``p  ``# compound interest = amount - principal amount``# printing compound interest value``print``(ci)`

Output

```133.0992000000001
```

Time Complexity: O(1) since no loop is used the algorithm takes up constant time to perform the operations
Auxiliary Space: O(1) since no extra array is used so the space taken by the algorithm is constant

Please refer complete article on Program to find compound interest for more details!

Method #4:  using for loop:

## Python3

 `def` `compound_interest(principal, rate, time):``    ``Amount ``=` `principal``    ``for` `i ``in` `range``(time):``        ``Amount ``=` `Amount ``*` `(``1` `+` `rate``/``100``)``    ``CI ``=` `Amount ``-` `principal``    ``print``(``"Compound interest is"``, CI)``# Driver Code``compound_interest(``1200``, ``5.4``, ``2``)``#This code is contributed by Jyothi pinjala`

Output

```Compound interest is 133.0992000000001
```

Time complexity: O(1)
Auxiliary Space: O(1)

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