What is the compound interest on USD 10000 in 2 years at 4% per annum if the interest is compounded semi annually?

The sooner you start to save, the more you'll earn with compound interest.

How compound interest works

Compound interest is the interest you get on:

  • the money you initially deposited, called the principal
  • the interest you've already earned

For example, if you have a savings account, you'll earn interest on your initial savings and on the interest you've already earned. You get interest on your interest.

This is different to simple interest. Simple interest is paid only on the principal at the end of the period. A term deposit usually earns simple interest.

Save more with compound interest

The power of compounding helps you to save more money. The longer you save, the more interest you earn. So start as soon as you can and save regularly. You'll earn a lot more than if you try to catch up later.

For example, if you put $10,000 into a savings account with 3% interest compounded monthly:

  • After five years, you'd have $11,616. You'd earn $1,616 in interest.
  • After 10 years you'd have $13,494. You'd earn $3,494 in interest.
  • After 20 years you'd have $18,208. You'd earn $8,208 in interest.

Compound interest formula

To calculate compound interest, use the formula:

A = P x (1 + r)n

A = ending balance
P = starting balance (or principal)
r = interest rate per period as a decimal (for example, 2% becomes 0.02)
n = the number of time periods

How to calculate compound interest

To calculate how much $2,000 will earn over two years at an interest rate of 5% per year, compounded monthly:

1. Divide the annual interest rate of 5% by 12 (as interest compounds monthly) = 0.0042

2. Calculate the number of time periods (n) in months you'll be earning interest for (2 years x 12 months per year) = 24

3. Use the compound interest formula

A = $2,000 x (1+ 0.0042)24
A = $2,000 x 1.106
A = $2,211.64

What is the compound interest on USD 10000 in 2 years at 4% per annum if the interest is compounded semi annually?

Lorenzo and Sophia compare the compounding effect

Lorenzo and Sophia both decide to invest $10,000 at a 5% interest rate for five years. Sophia earns interest monthly, and Lorenzo earns interest at the end of the five-year term.

After five years:

  • Sophia has $12,834.
  • Lorenzo has $12,500.

Sophia and Lorenzo both started with the same amount. But Sophia gets $334 more interest than Lorenzo because of the compounding effect. Because Sophia is paid interest each month, the following month she earns interest on interest.

Simple Interest: A = P(1+rt)

P: the principal, the amount invested A: the new balance t: the time r:the rate, (in decimal form)

Ex1: If $1000 is invested now with simple interest of 8% per year. Find the new amount after two years.

P = $1000, t = 2 years, r = 0.08. A = 1000(1+0.08(2)) = 1000(1.16) = 1160

Compound Interest:

P:the principal, amount invested A: the new balance t: the time r:the rate, (in decimal form) n: the number of times it is compounded. Ex2:Suppose that $5000 is deposited in a saving account at the rate of 6% per year. Find the total amount on deposit at the end of 4 years if the interest is:

P =$5000, r = 6% , t = 4 years

a) simple : A = P(1+rt)

A = 5000(1+(0.06)(4)) = 5000(1.24) = $6200

b) compounded annually, n = 1:

A = 5000(1 + 0.06/1)(1)(4) = 5000(1.06)(4) = $6312.38

c) compounded semiannually, n =2:

A = 5000(1 + 0.06/2)(2)(4) = 5000(1.03)(8) = $6333.85

d) compounded quarterly, n = 4:

A = 5000(1 + 0.06/4)(4)(4) = 5000(1.015)(16) = $6344.93

e) compounded monthly, n =12:

A = 5000(1 + 0.06/12)(12)(4) = 5000(1.005)(48) = $6352.44

f) compounded daily, n =365:

A = 5000(1 + 0.06/365)(365)(4) = 5000(1.00016)(1460) = $6356.12

Continuous Compound Interest:

Continuous compounding means compound every instant, consider investment of 1$ for 1 year at 100% interest rate. If the interest rate is compounded n times per year, the compounded amount as we saw before is given by: A = P(1+ r/n)nt
the following table shows the compound interest that results as the number of compounding periods increases:

P = $1; r = 100% = 1; t = 1 year

Compounded Number of periods per year Compound amount
annually 1 (1+1/1)1 = $2
monthly 12 (1+1/12)12 = $2.6130
daily 360 (1+1/360)360 = $2.7145
hourly 8640 (1+1/8640)8640 = $2.71812
each minute 518,400 (1+1/518,400)518,400= $2.71827

As the table shows, as n increases in size, the limiting value of A is the special number

e = 2.71828

If the interest is compounded continuously for t years at a rate of r per year, then the compounded amount is given by:

A = P. e rt

Ex3: Suppose that $5000 is deposited in a saving account at the rate of 6% per year. Find the total amount on deposit at the end of 4 years if the interest is compounded continuously. (compare the result with example 2)

P =$5000, r = 6% , t = 4 years A = 5000.e(0.06)(4) = 5000.(1.27125) = $6356.24

Ex4: If $8000 is invested for 6 years at a rate 8% compounded continuously, find the new amount:

P = $8000, r = 0.08, t = 6 years. A = 8000.e(0.08)(6) = 8000.(1.6160740) = $12,928.60

Equivalent Value:

When a bank offers you an annual interest rate of 6% compounded continuously, they are really paying you more than 6%. Because of compounding, the 6% is in fact a yield of 6.18% for the year. To see this, consider investing $1 at 6% per year compounded continuously for 1 year. The total return is: A = Pert = 1.e(0.06)(1) = $1.0618 If we subtract from $1.618 the $1 we invested, the return is $0.618, which is 6.18% of the amount invested. The 6% annual interest rate of this example is called the nominal rateThe 6.18% is called the effective rate.
  • If the interest rate is compounded continuously at an annual interest rate r, then Effective interest rate: = er - 1

  • If the interest rate is compounded n times per year at an annual interest rate r, then Effective interest rate = (1+r/n)n - 1
Ex5: Which yield better return: a) 9% compounded daily or b) 9.1% compounded monthly? a) effective rate = (1+0.09/365)365 - 1 = 0.094162 b) effective rate = (1+0.091/12)12 - 1 = 0.094893 the second rate is better.

Ex6: An amount is invested at 7.5% per year compounded continuously, what is the effective annual rate?

the effective rate = er - 1 = e 0.075 - 1 = 1.0079 - 1 = 0.0779 = 7.79%

Ex7: A bank offers an effective rate of 5.41%, what is the nominal rate?

er - 1 = 0.0541 er = 1.0541 r = ln 1.0541 then r = 0.0527 or 5.27%

Present Value:

If the interest rate is compounded n times per year at an annual rate r, the present value of a A dollars payable t years from now is:

What is the compound interest on USD 10000 in 2 years at 4% per annum if the interest is compounded semi annually?

If the interest rate is compounded continuously at an annual rate r, the present value of a A dollars payable t years from now is

P = A. e-rt

Ex8: how much should you invest now at annual rate of 8% so that your balance 20 years from now will be $10,000 if the interest is compounded a) quarterly: P = 10,000.(1+0.08/4)-(4)(20)= $ 2,051.10 b) continuously: P = 10,000.e-(0.08)(20) = $2.018.97

4.3: The Growth, Decline Model:

Same formulas will be applied for population, cost ...:

Growth: P(t) = Po . ekt

Decline: P(t) = Po . e-kt

  • P(t): the new balance the new population the new price ...
  • Po: the original balance the original population the original price
  • k: the rate of change the growth, decline rate the interest rate
  • t: the time (years, days...)

For compounded continuously, the time T it takes to double the price, population or balance using k as the rate of change, the growth rate or the interest rate is given by:

===>

Note: the time it takes to triple it is T = ln3/k and so on..., (only if it is compounded continuously).

Ex9: The growth rate in a certain country is 15% per year. Assuming exponential growth :

a) find the solution of the equation in term of Po and k. b) If the population is 100,000 now, find the new population in 5 years. c) When will the 100,000 double itself? Answer: a) Po. e 0.15t; b) 211,700; c) 4.62 years

Ex10: If an amount of money was doubled in 10 years, find the interest rate of the bank.

Answer: 6.93%

Ex11: In 1965 the price of a math book was $16. In 1980 it was $40. Assuming the exponential model :

a) Find k (the average rate) and write the equation. b) Find the cost of the book in 1985. c) After when will the cost of the book be $32 ? Answer: a) 6.1%; b) $ 54.19; c) T = 11.36 years

Ex12: How long does it take money to triple in value at 6.36% compounded daily?

Answer: 17.27 years

Ex13: A couple want an initial balance to grow to $ 211,700 in 5 years. The interest rate is compounded continuously at 15%. What should be the initial balance?

Answer: $100,000

Ex14: The population of a city was 250,000 in 1970 and 200,000 in 1980 (Decline). Assuming the population is decreasing according to exponential-decay, find the population in 1990.

Answer: 160,000

What is the compound interest on USD 10000 in 2 years at 4 per annum?

10000; Rate = 2% per half-year; Time = 2 years = 4 half-years. Amount = Rs [10000 * 1+2/1004 ] = Rs10000 * 51/50 * 51/50 * 51/50 * 51/50 = Rs. 10824.32.

What is the compound interest on 10000 in 2 years at 4% per annum if the interest is compounded semi annually?

= ₹(10824.32 - 10000) = ₹824.32. Q. Find the compound interest on Rs. 10,000 in 2 years at 4% per annum , the interest being compounded half yearly.

What is the difference between the compound interests on 10000 for 2 years at 5% per annum compounded annually and half yearly?

∴ Difference between interest compounded yearly and half yearly is Rs. 57.81.

What is the compound interest on 10000 for 2 years at 10% per annum?

Compound Interest would be 12100rs.