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Time value of money

Time value of money is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Time value of money rather than just read about it. In short: The time value of money refers to the idea that there is generally a greater benefit to receiving a sum of money now rather than an identical sum later. It may be seen as an implication of the later developed concept of time preference.

Time value of money — main illustration
Time value of money — illustration

Key takeaways

  • Time value of money belongs to engineering; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Time value of money to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Time value of money from memory before moving on to harder problems.

Reference excerpt

The time value of money refers to the idea that there is generally a greater benefit to receiving a sum of money now rather than an identical sum later. It may be seen as an implication of the later developed concept of time preference. The time value of money refers to the observation that it is better to receive money sooner than later. Money you have today can be invested to earn a positive rate of return, producing more money tomorrow. Therefore, a dollar today is worth more than a dollar in the future. The time value of money is among the factors considered when weighing the opportunity costs of spending rather than saving or investing money. As such, it is among the reasons why interest is paid or earned: interest, whether it is on a bank deposit or debt, compensates the depositor or lender for the loss of their use of their money. Investors are willing to forgo spending their money now only if they expect a favorable net return on their investment in the future, such that the increased value to be available later is sufficiently high to offset both the preference to spending money now and inflation (if present); see required rate of return.

Overview The time value of money compares cash flows that occur at different dates by converting them to a single valuation date (often called “time 0”). In a simple discrete-time model, time is measured in equal-length periods t = 0 , 1 , 2 , … {\displaystyle t=0,1,2,\dots } and a constant effective interest rate i {\displaystyle i} is applied once per period. If an amount P V {\displaystyle \mathrm {PV} } is invested at time 0, its value after n {\displaystyle n} periods (the future value) is

F V = P V ( 1 + i ) n . {\displaystyle \mathrm {FV} =\mathrm {PV} (1+i)^{n}.}

Discounting reverses this relationship, such that the present value of a sure amount F V {\displaystyle \mathrm {FV} } due at time n {\displaystyle n} is

P V = F V ( 1 + i ) − n = F V ( 1 + i ) n . {\displaystyle \mathrm {PV} =\mathrm {FV} (1+i)^{-n}={\frac {\mathrm {FV} }{(1+i)^{n}}}.}

The factor ( 1 + i ) n {\displaystyle (1+i)^{n}} is the accumulation factor over n {\displaystyle n} periods, and ( 1 + i ) − n {\displaystyle (1+i)^{-n}} is the corresponding discount factor. For a sequence of dated cash flows C F t {\displaystyle \mathrm {CF} _{t}} (positive for receipts and negative for payments), present value is the discounted sum of each cash flow:

P V = ∑ t = 0 n C F t ( 1 + i ) t . {\displaystyle \mathrm {PV} =\sum _{t=0}^{n}{\frac {\mathrm {CF} _{t}}{(1+i)^{t}}}.}

This discounted-sum form underlies net present value calculations used in valuation and capital budgeting. Nominal and real analyses must be kept consistent. Nominal cash flows are discounted at nominal rates, while real cash flows (with general inflation removed) are discounted at real rates; mixing conventions changes results mechanically even when the underlying economics is unchanged.

… excerpt ends here. Continue reading the full article.

Illustrations

Time value of money: The present value of $1,000, 100 years into the future. Curves represent constant discount rates of 2%, 3%, 5%, and 7%.
The present value of $1,000, 100 years into the future. Curves represent constant discount rates of 2%, 3%, 5%, and 7%.

Worked examples

Example 1 — a first encounter with Time value of money

Start with the simplest possible case. Write down what Time value of money claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Time value of money before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Time value of money ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Time value of money

In research
Time value of money appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Time value of money in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Time value of money is common in secondary-school and first-year university syllabi. It links to neighbouring topics Actuarial science, Engineering economics, Interest, so understanding it makes those chapters shorter.
In everyday life
Look for Time value of money outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Time value of money in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Time value of money means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Time value of money out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Time value of money in simple terms?

The time value of money refers to the idea that there is generally a greater benefit to receiving a sum of money now rather than an identical sum later. It may be seen as an implication of the later developed concept of time preference.

Why does Time value of money matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Time value of money?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Time value of money.

Tags

  • Actuarial science
  • Engineering economics
  • Interest
  • Intertemporal economics
  • Money

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