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Learn about compound interest, discrete and continuous compounding, effective annual yield, calculating values, yields, and rates with examples. Exploring logarithms for compound interest calculations.
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Project 2- Stock Option Pricing • Mathematical Tools -Today we will learn Compound Interest
Compounding • Suppose that money left on deposit earns interest. • Interest is normally paid at regular intervals, while the money is on deposit. • This is called compounding.
Compound Interest • Discrete Compounding -Interest compounded n times per year • Continuous Compounding -Interest compounded continuously
Compound Interest Discrete Compounding P- dollars invested r -an annual rate n- number of times the interest compounded per year t- number of years F- dollars after t years.
Yield for Discrete Compounding • The annual rate that would produce the same amount as in discrete compounding for one year. • Such a rate is called an effective annual yield,annual percentage yield, or just the yield. Compunded n times for one year Compounded once a year for one year
Yield for Discrete Compounding Interest at an annual rate r, compounded n times per year has yield y.
Discrete CompoundingExample 1 • What is the value of $74,000 after • 3-1/2 years at 5.25%,compounded monthly? • (ii) What is the effective annual yield?
Example1 (i) Using Discrete Compounding formula Given P=$74,000 r=0.0525 n=12 t=3.5 Goal- To find F
Example 1 (ii) Using yield formula Given r=0.0525 n=12 Goal- To find y
Discrete CompoundingExample 2 (i)What is the value of $150,000 after 5 years at 6.2%, compounded quarterly? (ii) What is the effective annual yield?
Example 2 (i) Using Discrete Compounding formula Given P=$150,000 r=0.062 n=4 t=5 Goal- To find F
Example 2 (ii) Using yield formula Given r=0.062 n=4 Goal- To find y
Annual rate for Discrete Compounding Interest compounded n times per year at a yield y, has an annual rate r.
Discrete CompoundingExample 3 • What rate, r, compounded monthly, • will yield 5.25%?
Example 3 (i) Using Annual rate formula Given y=0.0525 n=12 Goal- To find r
The value of P dollars after t years, when compounded continuously at an annual rate r,is F = Pert Compound Interest Continuous Compounding
Yield for Continuous Compounding Interest at an annual rate r, compounded continuously has yield y.
ContinuousCompoundingExample 1 (i)Find the value, rounded to whole dollars, of $750,000 after 3 years and 4 months, if it is invested at a rate of 6.1% compounded continuously. (ii) What is the yield, rounded to 3 places, on this investment?
Example1 • Using Continuous • Compounding formula • Given • P=$750,000 • r=0.061 • t=(40/12) • Goal- To find F F = Pert F = 750,000e0.061(40/12) =$ 919,111
Example 1 (ii) Using yield formula Given r=0.061 Goal- To find y
Logarithms • Why do we need logarithms for compound interest ? • To find r (since r is an exponent) Recall: yield formula for continuous compounding
Review of Logarithms • For any base b, the logarithm function logb (x) • The equations u = bv and v = logbu are equivalent • Eg: 100=102 and 2=log10100 are equivalent • Two types -Common Logarithms (base is 10) -Natural Logartihms (base is e)- Notation: ln
Review of Logarithms 1.The logarithm logb(x) function is the INVERSE of expb(x) 2. logb(x) is defined for any positive real number x
Review of Logarithms The basic properties of exponents, yield properties for the logarithm functions. bubv = bu+v and (bu)v = buv, logb(uv) = logbu + logbv logb(u/v) = logbu logbv logbuv = vlogbu.
Review of Logarithms • ln u = ln v if and only if u=v • Most commonly used to obtain solution of equations • We can transform an equation into an equivalent form by taking ln of both sides
Review of LogarithmsExample1 Find the annual rate, r, that produces an effective annual yield of 6.00%, when compounded continuously.
Example 1 (ii) Using yield formula Given y=6.00% Goal- To find r Taking ln on both sides
Review of LogarithmsExample 2 Find the annual rate, r, that produces an effective annual yield of 5.15%, when compounded continuously. Round your answer to 3 places.
Example 2 (ii) Using continuous compounding formula Given y=5.15% Goal- To find r Taking ln on both sides
Review of LogarithmsExample 3 How long will it take $10,000 to grow to $15,162.65 if interest is paid at an annual rate of 2.5% compounded continuously?
Example 3 (ii) Using yield formula Given F=$15,162.65 P=$10,000 r=0.025 Goal- To find t
Value of Money Discrete compounding Recall • Present value (P) and Future value(F) of money • We need to rearrange the formula to find P The present value of money for discrete compounding
Value of Money Continuous compounding Recall • Present value (P) and Future value(F) of money • We need to rearrange the formula to find P The present value of money for continuous compounding
Ratio (R) • Under continuous compounding-The ratio of the future value to the present value • This allows us to convert the interest rate for a given period to a ratio of future to present value for the same period
Recall- Class Project We suppose that it is Friday, January 11, 2002. Our goal is to find the present value, per share, of a European call on Walt Disney Company stock. • The call is to expire 20 weeks later • strike price of $23. • stock’s price record of weekly closes for the past 8 years(work basis). • risk free rate 4% (this means that on Jan 11,2002 the annual interest rate for a 20 week Treasury Bill was 4% compounded continuously)
Project Focus I • Walt Disney- r =4%, compounded continuously The weekly risk-free rate for the Walt Disney The risk-free weekly ratio for the Walt Disney
Project Focus II • Suppose we know the future value (fv) for our 20 week option at the end of 20 weeks • risk-free rate annual interest 4% • Can find the Present value (pv)