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Unit 10 · Lesson 2 Money math

$1,000 now or $1,100 later? Now wins.

The bike shop had a great year, and the owner offers you a bonus. You can take $1,000 today, or $1,100 in 2 years. $1,100 looks bigger. But your savings account pays 5% a year. Put the $1,000 in today and in 2 years it grows to $1,102.50, more than $1,100. Money you have now can start earning right away. That's the time value of money, and it's behind every loan, investment, pension and lottery payout.

What

A dollar today is worth more than a dollar later, because today's dollar can earn interest in the meantime.

Why

It lets you compare money at different times: a bonus now or later, a lump sum or payments, a car loan or cash.

How

Move every amount to the same moment. Grow today's money forward, or shrink future money back to today.

Who

Corporate finance analysts use it to decide which projects to fund. Bankers price loans with it. Financial planners use it to compare pension and payout choices.

The later offer: $1,100 Today1 year2 years $1,000$1,050$1,102.50 $ +5% a year money now gets a head start

What you're looking at: the $1,000 bonus taken today and saved at 5% a year. After 1 year it's $1,050; after 2 years, $1,102.50. The dashed line is the $1,100 you'd get by waiting. Taking the money now ends up $2.50 ahead.

01 See it

Moving money through time.

To compare amounts at different times, bring them to the same moment. You can go forward (future value) or back (present value). It's the same math, run in opposite directions.

Why a dollar now beats a dollar later

The time value of money comes from three things. Money now can earn interest. Inflation (Lesson 9.1) makes later dollars buy less. And a promise of money later has risk: it might not arrive.

In this example
Your bonus
The $1,000 today can sit at 5% for 2 years. The $1,100 can't earn anything until you get it.

Future value: growing money forward

Future value is what today's money grows to. It's the compound growth formula from Lesson 10.1.

Future value = today's amount × (1 + rate)years
In this example
$1,000 today at 5%
$1,000 × 1.05 × 1.05 = $1,102.50 in 2 years. That's the future value.

Present value: shrinking money back

Present value runs the math in reverse: how much a future amount is worth today. Turning future money into today's money is called discounting.

Present value = future amount(1 + rate)years
In this example
$1,100 in 2 years at 5%
$1,1001.05 × 1.05 = $1,1001.1025 = $997.73 today. That's less than $1,000, so taking the money now wins.

The discount rate

The rate you use is the discount rate: what you could earn on the money elsewhere. It's an opportunity cost (Lesson 8.1). The higher the rate, or the longer the wait, the less future money is worth today.

In this example
$1,100 in 2 years, at 5%
Worth $997.73 today.
Same, at 2%
$1,1001.02 × 1.02 = $1,057.29 today. With a lower rate, waiting would win.

A stream of payments

Many deals pay a set amount every year, like a pension or a lottery payout. A stream of equal payments is called an annuity. Its present value is just the present value of each payment, added up.

In this example
$100 a year for 3 years, at 10%
$1001.10 + $1001.102 + $1001.103 = $90.91 + $82.64 + $75.13 = $248.69 today, not $300.

What you're looking at: the $1,000 bonus now against a later offer you set. Both bars are in today's dollars: the second bar is the later offer discounted back to today. Whichever bar is longer is the better deal.

02 Hear it

Two minutes. Just listen.

Tap any line to jump to it.

03 Play it

Now or later?

Eight offers. Each one gives you the numbers. Work out what each choice is worth at the same moment, then tap your answer. One try each.

Offer 1 of 8
Right0 of 0

    What you're looking at: made-up offers. Each lists the amounts, the wait and the rate you could earn, then asks one question.

    04 Break it down

    The logic, step by step.

    Every now-or-later question takes the same three steps.

    Step 1: Pick the rate

    The rate = what you could earn on the money instead
    In this example
    Your savings account
    5% a year.

    Step 2: Move both amounts to the same moment

    Forward: × (1 + rate) each year   ·   back: divide by (1 + rate) each year
    In this example
    Both to today
    $1,000 stays $1,000. $1,1001.1025 = $997.73.
    Or both to year 2
    $1,000 × 1.1025 = $1,102.50. $1,100 stays $1,100.

    Step 3: Compare

    Bigger value at the same moment = better deal
    In this example
    Either way
    Now wins by $2.27 in today's dollars, or $2.50 in year-2 dollars. Same answer.

    Worked example: when does waiting win?

    1. The question. How big would the 2-year offer need to be to beat $1,000 now?
    2. The rate. 5% a year, your savings account.
    3. Grow $1,000 forward. $1,000 × 1.05 × 1.05 = $1,102.50.
    4. The answer. Any offer over $1,102.50 in 2 years beats $1,000 now. At exactly $1,102.50 they're worth the same.
    5. The lesson. "Bigger later" only wins if it's bigger by more than the money could earn in the meantime.
    05 Nature link

    Squirrels know.

    Gray squirrels treat acorns differently depending on how well they keep. White oak acorns sprout soon after they fall, so they lose value fast. Squirrels tend to eat those right away. Red oak acorns stay dormant until spring, so they hold their value. Squirrels are more likely to bury those for winter.

    White oaksprouts soon:eat now Red oakkeeps:bury for later Use now, or save for later?

    What you're looking at: an illustration, not data. A squirrel with white oak acorns on the left, which it tends to eat now, and red oak acorns on the right, which it tends to bury for winter.

    Why this sticks. Whether to wait depends on what holds its value over time. Money in savings keeps growing, so saving it works. A promise that loses value while you wait, like a later payment in an inflation-heavy year, is worth less than it looks.

    06 Notes

    The page you'd copy down.

    • Time value of money: a dollar now beats a dollar later (interest, inflation, risk).
    • Future value = today × (1 + rate)years. $1,000 at 5% for 2 years = $1,102.50.
    • Present value = future amount(1 + rate)years. $1,100 in 2 years at 5% = $997.73.
    • Discount rate = what you could earn elsewhere. Higher rate or longer wait → lower present value.
    • Annuity: add up the present value of each payment. $100 a year for 3 years at 10% = $248.69.
    • To compare: move every amount to the same moment, then pick the bigger one.

    Fill in the blanks

    1. $1,000 at 10% for 1 year grows to $.
    2. Turning a future amount into today's value is called .
    3. The rate you use to bring future money back to today is the rate.
    4. A higher rate makes the present value .
    07 Together

    Grab a friend or a study group.

    Would you wait?

    Each person says the smallest amount in 1 year they'd take instead of $100 today. Compare your answers with what a 5% rate says: $105.

    Break the tie

    Use the slider above. One person sets the later offer; the other finds the rate where now and later are worth the same.

    Lottery debate

    Lump sum or yearly payments? Argue both sides, then check the math in the job task below.

    08 On your own

    Just you and your money.

    These stay on this device. Nobody else sees them.

    When did you last choose "now" over "later" with money? Would the math have agreed?
    What rate could your money earn right now? That's your discount rate. Where would you put it?
    What's one thing you could start today that would be worth much more to you in 10 years?

    09 Check

    Exam-style questions.

    Written the way a college exam would ask them. Each right answer on the first try is worth 10 xp.

    On the job: you're a financial planner

    Your client just won the lottery. They must pick one way to be paid:

    • Lump sum: $600,000 today.
    • Payments: $50,000 a year for 20 years, $1,000,000 in total.
    • Present value of the payments at 5%: $623,111.
    • Present value of the payments at 7%: $529,701.

    Your task: which choice is worth more today if your client can earn 5% a year? What if they can earn 7%? Why isn't $1,000,000 the real value of the payments?

    See a model answer

    At 5%: the payments are worth $623,111 today, more than the $600,000 lump sum. Take the payments, by $23,111.

    At 7%: the payments are worth $529,701 today, less than $600,000. Take the lump sum, by $70,299.

    Why not $1,000,000: most of the payments arrive years from now. Each one is discounted back to today, and the last ones shrink the most.

    The real question: what can your client actually earn, and will they invest the lump sum or spend it? Taxes also matter, so a tax pro should check the final numbers.

    10 Where it leads

    Every money choice has a clock.

    Percentages and growthUnit 10 · compound growth Savings that earn moreUnit 3 · your rate Scarcity and trade-offsUnit 8 · opportunity cost You are here Time value of money Money psychologyNext lesson · Unit 10

    What you're looking at: a map of where this lesson fits in the course. Read it left to right: the lessons it builds on, this lesson in the middle, and the lesson that comes next.

    • Back · Unit 10The math of percent and growth
    • Back · Unit 3Make your savings earn more
    • Back · Unit 8Every choice has a price tag
    • You are hereThe time value of money
    • Next · Unit 10Money psychology
    Next lesson: Why we make bad money choices →Course map