RedCrab Math Tutorial

Calculation of Interest

The interest calculation is an extension of the percentage calculation. Interest is a percent value of one underlying or principal.

Base of the percentage calculation is the formula:

Interest formula

Z = Interest

K = Principal

P = Interest rate

The formula can be changed for the value you are looking for

Interest rate: Interest rate formula

Interest: Interest calculation

Principal: Principal formula


Calculate interest income

This example calculates the interest earned on investing 3000$ for one year at a fixed rate of 3%.
Given is the interest rate P = 3 and the capital = 3000.
We are looking for the interest income Z.
The interest income is calculated according to the formula:calculate interest income$

Calculate interest rate

This example calculates the interest rate, which is required to receive $ 150 interest in one year, from a capital of $ 3,000
The capital K = 300 and the interest income Z = 150 are known.
We are looking for the interest rate P.
Calculated according to the formula: calculate interest rate formula

Calculate starting capital

What amount must be invested in order to receive an interest income of 200 $ at a rate of 5%? This question should be solved in this task.
The interest rate of P = 5% and the interest income Z = 200 $ are known
We are looking for starting capital K.

It is calculated according to the formula: calculate starting capital formula$


Calculate interest income daily

For example, suppose you want to invest $ 5,000 for 2 months at an annual interest rate of 5%. For this, the interest must be calculated on a daily basis. The formula for calculating the interest income is extended accordingly by the number of days = t. For each month, 30 days, so 360 days for 1 year are assume.

The advanced formula is: calculate Interest per day formula

The capital K = 5000, the interest rate P = 5 and the number of days t = 60 are known
We are looking for interest income Z.

This is calculated: calculate Interest per day$



Integer and Real Numbers
Complex Numbers
Polar Coordinates
Roots and Power
Percentage Calculation
Interest Calculation
Absolute Value of a Number
Euclidean division
Modulo - Remainder of a division
Vector Calculation
Matrices Definition
Matrices Calculation
Matrices & Simultaneous Equations
Matrices Determinants
Row Operations of Matrices
Matrices and Geometry, Reflection
Matrices and Geometry, Rotation


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