What is the difference between the compound interest, when interest is compounded 5-monthly

Calculating Interest and Excel Functions:

In the real world, interest is often compounded more than once a year. In many cases, it is compounded monthly, which means that the interest is added back to the principal each month.

In order to calculate compounding more than one time a year, we use the following formula:

\({\text{A}} = {\text{P}}(1+\frac{\text{r}}{\text{n}})^{\text{nt}}\)

A = Amount (ending amount)
P = Principal (beginning amount)
r = Rate (annually) as a decimal
t = Time in years
n = Number of compounding periods per year

The following video will explain a little more about each of the formulas we have learned to calculate interest so far and how they are related.

Video Source (05:01 mins) | Transcript

The following video demonstrates how to do the compound interest calculation using the order of operations. It also demonstrates how to enter the numbers into a calculator in order to avoid rounding errors.

How to Avoid Rounding Errors

Avoid rounding errors by NOT rounding until the final answer. Do this by following the order of operations and using all the digits in the calculator from each previous step.

Video Source (07:57 mins) | Transcript

Practice Problems

  1. If you invest $1000 in an account that pays 9% interest annually, compounded monthly, what is the total amount of money that you would have at the end of one year? (Hint: In this case, n = 12 because it is compounding monthly, but t = 1 because we are calculating for 1 year.)

  2. Suppose that you invest $2000 in an account that pays 4% interest annually, compounded monthly. How much money would you have in the account after three years?
  3. (Hint: n = 12 and t = 3.)
  4. Look at the answer to question 2. How much interest was earned over the three years?

  5. Suppose that you invest $2000 in an account that pays 8% interest annually, compounded monthly. How much money would you have in the account after three years?

  6. Look at the answer to question 4. How much interest was earned over the three years?

  7. Compare the answers to questions 3 and 5. When the interest rate is doubled from 4% to 8%, What happens to the amount of compound interest earned after three years?
    1. Exactly the same
    2. Less than doubled
    3. Exactly doubled
    4. More than doubled


Compound interest is an interest of interest to the principal sum of a loan or deposit. The concept of compound interest is the interest adding back to the principal sum so that interest is earned during the next compounding period.

The formula is given as:

Monthly Compound Interest = Principal

\(\begin{array}{l}(1+\frac{Rate}{12})^{12*Time}\end{array} \)

– Principal

Solved Example

Question: A sum of Rs. 5000 is borrowed and the rate is 8%. What is the monthly compound interest for 2 years?

Solution:

Monthly Compound Interest = Principal

\(\begin{array}{l}(1+\frac{Rate}{12})^{12*Time}\end{array} \)

– Principal

Monthly Compound Interest = 5000

\(\begin{array}{l}(1+\frac{8}{100*12})^{12*2}\end{array} \)

– 5000

Monthly Compound Interest = 5000 × 1.1738 – 5000

= 5869 – 5000 = 869

The monthly compound interest for 2 years is Rs. 869.

The monthly compound interest formula is used to find the compound interest per month. Compound interest is widely known as interest on interest. Compound interest for the first period is similar to the simple interest but the difference occurs in and from the second period of time. From the second period, the interest is also calculated on the interest thus earned on the previous period of time, that is why it is known as interest on interest. Let us learn more about the monthly compound interest formula along with solved examples.

What Is the Monthly Compound Interest Formula?

The monthly compound interest formula is also known as the formula of interest on interest calculated per month, the interest is added back to the principal each month. Total compound interest is the final amount excluding the principal amount. 

What is the difference between the compound interest, when interest is compounded 5-monthly

Monthly Compound Interest Formula

The formula for the compound interest is derived from the difference between the final amount and the principal, which is: CI = Amount - Principal. The formula of monthly compound interest is:

CI = P(1 + (r/12) )12t - P

Where,

  • P is the principal amount,
  • r is the interest rate in decimal form,
  • t is the time.

Derivation of Monthly Compound Interest Formula

The formula for calculating the compound interest is as,

CI = P (1 + r/100)n

  • P is the principal amount
  • r is the rate of interest
  • n is frequency or no. of  times the interest is compounded annually
  • t is the overall tenure.

If the time period for the calculation of interest is monthly, the interest is calculated for each month, and the amount is compounded 12 times a year as there are 12 months in a year. The formula to calculate the compound interest when the principal is compounded monthly is given as: 

 CI = P(1 + (r/12) )12t - P

Here the compound interest is calculated for a month (time period). Thus, the rate of interest r, is divided by 12 and the time period is 12 times.

What is the difference between the compound interest, when interest is compounded 5-monthly

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Examples Using Monthly Compound Interest Formula

Example1: If Sam lends $1,500 to his friend at an annual interest rate of 4.3%, compounded per month. Calculate the interest after the end of the year by using the compound interest formula.

Solution:  

To find: Compound interest accumulated after 1 year.

P = 1500, r = 0.043 (4.3%), n = 12 , and t = 1 (given)

Using monthly compound interest formula,

CI = P(1 + (r/n) )nt - P

Put the values,

CI = 1500(1 + (0.043/12))12 - 1500

CI = 65.786

Answer: The compound interest after 1 year will be $65.786.

Example 2: James borrowed $600 from the bank at some rate compounded per month and that amount becomes quadruple in 2 years. Calculate the rate at which James borrowed the money by using the monthly compound interest formula.

Solution:

To find: Interest rate

P = 600, n = 12, and t = 2, Amount = 2400 (given)

Using formula,

CI = Amount - Principal

Put the values,

CI = 2400 - 600 = 1800

Using monthly compound interest formula,

CI = P(1 + (r/12) )12t - P

 Put the values,

1800 = 600(1+ (r/12))12×2 - 600

4 = (1+ (r/12))24 

r = 71.4 

Answer: The Interest rate on the given amount of money is 71.4%.

Example 3: Calculate the monthly compound interest on the sum of $6000 borrowed at the rate of 10% for 2 years.

Solution:

To find: Monthly compound interest

P=$6000, r=10%, t=2years (given)

CI = P(1 + (r/12) )12t - P

Put the values,

= 6000(1+10/12)12×2 – 6000

= 7322.35 – 6000 = 1322.35

Answer: The monthly compound interest for 2 years is $1322.35 

FAQs on Monthly Compound Interest Formula

What Is the Monthly Compound Interest Formula in Math?

The monthly compound interest formula is used to find the compound interest per month. The formula of monthly compound interest is: CI = P(1 + (r/12) )12t - P where, P is the principal amount, r is the interest rate in decimal form, and t is the time.

How to Calculate Amount Using Monthly Compound Interest Formula?

There is a direct formula for the calculation of monthly compound interest. A = CI = P(1 + (r/12) )12t 

  • Step 1: Here we need to define the principal and the rate of interest at which the compound interest is calculated so check for the values of P, r and t.
  • Step: Put the values in the formula, A = CI = P(1 + (r/12) )12t 

What Is r In the Monthly Compound Interest Formula?

In the monthly compound interest formula, CI = P(1 + (r/12) )12t - P, r refers to the interest rate on the principal.

What Are the Components of the Monthly Compound Interest Formula?

The calculation of monthly compound interest requires us to know the principal, rate of interest, and the time period. 

What does 5% compounded mean?

Compound interest is the interest you earn on interest. This can be illustrated by using basic math: if you have $100 and it earns 5% interest each year, you'll have $105 at the end of the first year. At the end of the second year, you'll have $110.25.

What is the difference between compounded annually and monthly?

"12% interest" means that the interest rate is 12% per year, compounded annually. "12% interest compounded monthly" means that the interest rate is 12% per year (not 12% per month), compounded monthly. Thus, the interest rate is 1% (12% / 12) per month.

How do you find the difference in compound interest?

Then, find the amount for the compound interest compounded half-yearly by applying the formula A=P(1+r2×100)t×2. Then subtract the principal from the amount to get the interest. After that subtract the values of the interest to find the difference of the interest.

What is the difference between compound interest on Rs 5000 for 1.5 years at 4% per annum the interest is compounded yearly and half yearly?

Detailed Solution = Rs. (5000 × 26/25 × 51/50) = Rs. 5304.