An interactive reader · compound interest
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What time does
with money.
Each sentence below is a small financial story you can rewrite. Amber numbers are yours to edit: click one, type, or nudge it with ↑ ↓. Green numbers are what time does with them.
A $4 coffee, 365 days a year, invested instead at 7% a year, would grow to $0 after 20 years, on just $0 of skipped coffee.
Small habits
What everyday spending quietly adds up to
A $5 coffee, 300 days a year, is $0 a year, and $0 over 10 years.
A $4 latte, 7 days a week, sets you back $0 a week, $0 a month, and $0 a year.
A commute coffee, 5 days a week, 50 working weeks a year, is 0 cups: a $4 habit that really averages $0 a day, not $0, and costs $0 a year.
Even a modest $2 latte, 4 days a week, means $0 spent after 10 years.
A $8 pack of cigarettes a day burns through $0 a year, and $0 in a decade.
Paying a $35 late fee every month flushes $0 a year down the drain, and $0 over ten.
Saving
Steady deposits, given time
Save just $1 a day at a 7% return and after 30 years you'll be holding $0.
Start with $25,000, add $500 a month at 7% compounded monthly, and in 15 years the account holds $0.
A single $1,000 invested at 5% becomes $0 after 10 years, without adding a cent.
$150 a month at 10% quietly grows into $0 in 10 years.
At $5 a day and 10% returns, reaching $1,000,000 takes 0 years. Double it to $10 a day and you get there 0 years sooner.
Investing
Growth, rate, and patience
$1,000 in an index fund growing 10% a year becomes $0 after 40 years.
A $1,000 bet on a stock compounding at 31% is worth $0 ten years later, a total return of 0% over 10 years.
Choose the smaller house, invest the $6,000 yearly difference at 6%, and after 30 years you'd have $0. Hold it 20 more years and it's $0.
Rate matters more than it looks: $10,000 for 30 years at 10% becomes $0, but at 12.5% it becomes $0.
Withdraw the gains on $10,000 at 7% every year and you'll earn $0 in 40 years. Let them compound instead, and you'll earn $0.
Present value
What future money is worth today
At 10% interest, $1,100 a year from now is worth exactly $0 today.
A promise of $500 next year, discounted at 10%, is worth $0 right now.
$900 arriving in 3 years, at 10%, equals $0 in today's money.
A $10,000 lump sum due in 5 years, discounted at 7%, is the same as $0 today.
Every $1 you spend today is really $0 taken out of your pocket 20 years from now, at an 8% return.
Inflation & taxes
The quiet leak
An item that costs $100 today will cost $0 in 10 years at 3% inflation.
Put $100 under the mattress for 20 years at 3% inflation and it will only buy what $0 buys today.
To match the purchasing power of $60,000 today, in 20 years you'll need $0, assuming 3% inflation.
$100 at 5.05% APY shows $0 on your statement after 20 years, but with 3% inflation it's really worth $0.
A nominal nest egg of $350,000 arriving in 40 years, at 2.5% inflation, is only $0 in today's dollars.
Pay 28% tax on the interest and a 5.05% account really earns 0%; after 20 years, with 3% inflation, your $100 is worth just $0 in today's money.
Time
The other compounding currency
20 minutes a day is 0 hours a year, the same as 0 full eight-hour workdays. And 0 minutes a day is 0 hours a year.
2 hours of scrolling a day quietly consumes 0 hours a year: 0 entire days, awake and asleep.
Read just 10 pages a day and you'll finish 0 pages a year, about 0 books of 300 pages each.
Practicing 1 hour a day, reaching 10,000 hours of mastery takes 0 years; at 3 hours a day, only 0.
Earning $60,000 a year over 2,000 working hours means $0 an hour, so a $5 coffee costs 0 minutes of your life.
Starting early
Save early and often
Save $100 a month from age 18 at 6% and by 65 you'll have $0. Wait until 25 and you end up with only $0. That's $0 lost to 0 years of waiting.
Raise the return to 9% and the head start from 18 to 25, at $100 a month until 65, is worth $0, bought with just $0 of extra deposits.
Open a $350-a-month fund the day your baby is born, earning 7%, and by the time she starts university at 17.5 it holds $0.
A 25-year-old saving $200 a month at 7% retires at 65 with $0, and every single year of delay erases about $0 of it.
To retire at 65 with as much as a friend who saved $150 a month from age 20 at 7%, someone starting at 30 must put away $0 every month, 0× as much.
Reaching a goal
Working backwards from the number you want
To reach $50,000 in 10 years at 7%, you need to save $0 a month.
Hitting $1,000,000 by age 65 at 8% takes $0 a month if you start at 30, but $0 a month if you wait until 40.
Put weekly: $1,000,000 in 40 years at 7% is $0 a week, about $0 a day.
A $30,000 down payment in 5 years at 4% means setting aside $0 a month; under the mattress, it would take $0.
Already holding $10,000? Then reaching $100,000 in 15 years at 7% needs only $0 a month, instead of $0 from zero.
The big wins
The skeptic's view: decisions beat lattes
A fair objection to everything above: a handful of big decisions can outweigh years of small sacrifices.
Negotiate $1,000 off your next car and you've paid for 0 lattes at $5 each, almost 0 years of one every weekday morning.
How many lattes is that, anyway? A $2,500 impulse purchase equals 0 lattes at $5, one every day for 0 years.
Negotiating a salary just $5,000 higher, invested at 7% every year for 30 years, becomes $0, the biggest latte of all.
Overpay $20,000 on a house, at a 7% opportunity cost over 30 years, and you've lost $0, equal to 0 years of a daily $5 latte habit.
And yet: a $5 coffee, 300 days a year, is still $0. That's 0% of a $50,000 income. The honest answer is to do both: win the big negotiations and mind the habits.
Investing behavior
How you invest, not just how much
Slightly more advanced: three classic timing dilemmas, reduced to arithmetic.
Hand a $12,000 windfall to the market at once at 8% and it's $0 after 10 years. Drip it in over 12 months instead and you end with $0, a $0 price for the comfort of averaging in.
Stay fully invested at the market's historical 5.6% and $10,000 becomes $0 over 20 years, but investors who missed just the 10 best days earned about 2%, ending with $0. Half the outcome hid in a handful of days you can't predict.
Waiting in cash for a 10% dip while the market compounds at 8% only pays off if the dip arrives within 0 years. After that, the "expensive" market you refused to buy is still cheaper than your patience.
Housing
The biggest numbers most people ever touch
A $300,000 house appreciating 3% a year is worth $0 after 20 years. Renting instead, and investing the $60,000 down payment plus $500 a month of ownership savings at 8%, grows to $0. The winner lives entirely inside these assumptions.
On a $300,000 loan at 6%, the 30-year mortgage costs $0 a month and $0 in total interest; the 15-year costs $0 a month but only $0. The shorter loan buys back $0.
Put less down and invest the difference: keeping $45,000 in the market at 8% grows to $0 over 30 years, while borrowing that same amount at 6% costs $0 more in interest. The gap between the two rates decides who wins.
Overpaying the mortgage by $200 a month is a guaranteed return at your loan's 6%, worth $0 over 25 years. The same money invested at 8% reaches $0: a $0 edge, paid for in risk.
Debt
Compounding, working against you
On a $5,000 card at 24% APR, the interest alone is $0 a month; pay less than that and the debt is immortal. Pay $150 and you're free in 0 months with $0 of interest; $250 takes 0 months and $0.
Stretch a $30,000 student loan at 5% from 10 years to 25 and the payment falls from $0 to $0 a month, but the total interest jumps from $0 to $0.
Finance a $25,000 car at 8% for 5 years: $0 a month, and the car really costs $0; the $0 of interest is 0% of the sticker price.
Carrying $10,000 at a mortgage-like 4% costs $0 a year; the same balance on a 20% credit card costs $0, 0× as much. "Debt" is one word for two very different animals.
Putting $200 a month against a 20% debt is a guaranteed return at that rate, worth $0 over 5 years, while the same money invested at 8% reaches only $0. Kill high-interest debt first; the market can't reliably beat it.