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The present value of a dollar to be received in a year is
less than the present value of that dollar if it were received today. We call this the
time value of money. Financial
markets use spot curves, forward curves, discount curves and yield curves
to describe the time value of money. These are referred to collectively as
the fixed income term structure. This article defines these
notions.
A cash loan is a loan that
commences immediately. A spot loan is a loan that
commences spot. A
forward loan is one that commences on some
date later than spot. For example, in the Eurodollar markets a
three-month spot loan commences in two business days (spot) and matures
three months after that. A 2 7 forward loan commences two months from the
spot date and lasts for five months. With either type of loan, interest
can be paid periodically or it can be accumulated and paid at maturity.
A spot interest rate
for maturity m is an interest rate payable on a spot loan of
maturity m that accumulates interest to maturity. Spot rates are
sometimes called zero-coupon rates
because they are the rates of interest payable on obligations that
accumulate all interest to maturity.
Libor rates for maturities of a week
or more are spot rates. Exhibit 1 indicates
USD Libor rates for monthly
maturities as of March 1, 2004.
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1 month |
1.10000 |
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2 month |
1.11000 |
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3 month |
1.12000 |
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4 month |
1.13000 |
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5 month |
1.15000 |
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6 month |
1.17000 |
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7 month |
1.19375 |
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8 month |
1.22125 |
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9 month |
1.25000 |
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10 month |
1.29000 |
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11 month |
1.32875 |
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12 month |
1.36750 |
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Source:
BBA |
A spot curve (or
zero-coupon curve) is a graph of spot rates
as a function of maturity.
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Spot curve constructed from the Libor
rates of Exhibit 1. |
An n
(n + m) forward rate is an interest rate payable on a
forward loan that
commences n months from the spot date,
matures m months after that, and
accumulates interest to maturity.
If we have a spot curve, we can calculate forward rates.
Suppose we want the 3 5
forward USD Libor rate for March 1, 2004. We can calculate this from the
3-month and 5-month spot Libor rates. Let r denote the desired
forward rate. We use the fact that a 5-month spot loan is financially
equivalent to a 3-month spot loan combined with a 3 5
forward loan. With Libor, simple
compounding is used. Based on the 3-month and 5-month spot rates and day counts
as of March 1, we conclude
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(1 + .0112(92/360)) (1 + r (61/360)) = (1 + .0115(153/360)) |
[1] |
Solving for r, we obtain the forward rate as 1.19%.
Note that this exceeds both the spot rates, which are 1.12% and 1.15%.
This makes sense. If there are to be no
arbitrage
opportunities, the combined interest from the 3-month spot and forward
loans must equal the interest earned on the 5-month spot loan. If the rate
earned on the 3-month spot loan is lower than that earned on the
5-month spot loan, then the rate earned on the forward loan will have to
be greater than that earned on the 5-month spot loan.
A forward curve is a
graph of forward rates all for the same maturity but with different
forward periods. For example, a forward curve might indicate rates for 0 3,
1 4,
2 5,
3 6,
4 7,
... , 120 123
forward loans. This would be called a 3-month forward curve. Exhibit 3
indicates a 1-month forward curve calculated from the spot rates of
Exhibit 1.
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0x1 |
1.10000 |
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1x2 |
1.11927 |
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2x3 |
1.13754 |
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3x4 |
1.15735 |
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4x5 |
1.22402 |
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5x6 |
1.26254 |
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6x7 |
1.33145 |
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7x8 |
1.40115 |
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8x9 |
1.47255 |
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9x10 |
1.62928 |
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10x11 |
1.69269 |
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11x12 |
1.81135 |
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One-month forward rates calculated from
the spot Libor rates of Exhibit 1. |
These are graphed in Exhibit 4.
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One month forward curve constructed from the
spot Libor
rates of Exhibit 1. The curve is superimposed over the spot curve of
Exhibit 2. |
Note that spot and forward curves provide identical
information. If you have one, you can construct the other.
A third, also equivalent way to indicate the time value of
money is discount factors. When we
calculate the present value of some future cash flow, we are said to
discount that future cash flow. A
discount factor is the factor by which the future cash flow must be
multiplied to obtain the present value. For example, if a
EUR 100 payment to be made at
maturity m has present value EUR 89.4, the EUR discount factor for
maturity m is .894. Note that present values are often calculated
with a spot
value date. If this is the case,
discount factors reflect discounting to the spot date as opposed to the
current date.
Discount factors can be calculated from spot or forward
rates. As an example, from Exhibit 1, the March 1, 2004 USD spot 6-month
Libor rate was 1.17%. We calculate the corresponding discount factor as
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1 /
(1 + .0117(184/360)) = .99406 |
[2] |
This represents discounting from the date six months after
spot back to the spot date.
A discount curve is a
graph of discount factors for different maturities. Exhibit 5 indicates
discount factors calculated from the spot Libor rates of Exhibit 1. These
are graphed in Exhibit 6.
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1 month |
0.99905 |
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2 month |
0.99812 |
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3 month |
0.99715 |
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4 month |
0.99619 |
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5 month |
0.99514 |
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6 month |
0.99406 |
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7 month |
0.99295 |
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8 month |
0.99176 |
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9 month |
0.99054 |
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10 month |
0.98915 |
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11 month |
0.98771 |
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12 month |
0.98633 |
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Discount factors calculated from
the spot Libor rates of Exhibit 1. |
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Discount curve constructed from the spot
Libor rates of Exhibit 1. |
The fourth way the time value of money can be described is
with a yield curve. This is simply a
graph of bond
yields for various maturities. The curve is typically fit in
some manner to price data for bonds of various maturities trading close to
par and generally of the same credit quality. Yield curves are falling out
of use today. Widespread use of computers in finance makes spot curves,
forward curves and discount curves easier to construct and use in pricing
work. Also, while yields continue to be widely quoted for bonds, fixed
income markets are increasingly trading instruments other than bonds for
which yield is either a meaningless or not useful notion. Today, when
people speak of yield curves, they often mean spot curves.
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bond Securitized debt.
asset-liability
management Techniques for protecting a firm's solvency in the context of accrual accounting.
compound interest
Any of several methods of crediting interest in which interest is earned on interest.
duration and convexity
Risk metrics employed in fixed income markets.
gap analysis
A technique of asset-liability management used to assess interest rate risk or
liquidity risk.
interest
rate parity An arbitrage condition that must hold between the spot interest
rates of different currencies.
interest rate risk
Risk due to uncertain future interest rates.
interest rate
spreads Discusses credit spreads, liquidity spreads,
optionality spreads, etc. in the fixed income markets.
interest
rate swap A swap under which both cash flow streams are in the same currency and are defined as cash flow streams that might be associated with some fixed income obligations.
Libor
London interbank offered rate.
floater
A fixed income instrument whose coupon fluctuates with some designated reference
rate.
forward contract
A trade that is agreed to at one point in time but will
take place at some later time.
future
An exchange-traded derivative that is similar to a forward.
option-adjusted spread
Yield spread not attributable to embedded options.
return Any of a number of metrics for the
change in an asset's or portfolio's accumulated value
settlement Article discusses forward contracts among other related topics.
Treasury
security
US Federal Government debt obligation issued by the Department of Treasury.
yield
Any of several metrics of the income or return to be earned from an investment. |
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Questa (1999) is an introductory text
on fixed income and foreign exchange mathematics. Stigum and
Robinson (1996) is a detailed, hands-on guide to fixed income
computations with an emphasis on standard conventions for
calculating day counts, accrued interest, compounding, etc. James
and Webber (2000) is an intermediate-advanced text. All three
books are exceptional.
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