True cost of a purchase calculator

How the formula works

A price tag is only the sticker. What a purchase really costs you shows up in two other currencies — the hours of your life you traded to earn it, and the retirement money you gave up by not investing it. This tool prices any purchase in both.

Hours of work. Divide the price by what you actually earn per hour, after tax:

The denominator is deliberately your take-home pay — the money that actually lands in your account — not your gross salary. Taxes, payroll deductions and benefits never reach your wallet, so counting them would flatter the wage and undercount the hours. Priced against what you keep, the hours are honest.

Retirement money forgone. The same dollars, invested as a lump sum and left to compound until you retire, would grow to:

where \(r\) is the expected annual return as a decimal and \(t\) is the years between your age now and retirement. The calculator applies this as an effective monthly rate — the same compounding the compound interest tool uses — so a smooth curve connects today's price to its retirement-day value. The growth multiple is simply \((1+r)^{t}\): how many times over the money would multiply if you invested it instead of spending it.

The point is not that you should never spend. It is that a number on a tag hides both of these costs, and seeing them makes the trade conscious: this purchase is worth this many hours of my life and this much of my future — and sometimes the answer is still yes.

What each input means

Purchase price

The sticker price of the thing you are weighing. For something you would finance, use the total you will actually pay, interest included — that is the real outlay.

Annual take-home pay

Your pay after tax and deductions — what hits your bank account in a year. Using take-home rather than gross is what makes the hours honest: it is the money you genuinely trade your time for.

Hours worked per year

How many hours you work in a year. A standard full-time year is about 2,080 (40 hours × 52 weeks). If your real week is longer, or you want to count commuting and unpaid overtime as part of the price of the job, raise it — your true hourly wage falls, and every purchase costs more hours.

Your age

Your age today. Together with the retirement age it sets how long the money would have to compound — the single input that most changes the opportunity cost, because time is what compounding feeds on.

Retirement age

When you would stop working. The gap between this and your age now is the runway the foregone dollars would have to grow.

Expected annual return

The yearly return you assume the money would earn if invested. A long-run figure like 5–7% is a common starting point for a diversified portfolio; nothing guarantees it, and a lower number gives a more cautious opportunity cost.

A worked example

Take the worksheet's opening numbers: a $1,200 purchase, on $60,000 of take-home pay, working 2,080 hours a year, at age 30 with retirement at 65 and a 7% expected return.

• Your real hourly wage is $60,000 / 2,080 hours = $28.85 an hour.
• So the purchase costs $1,200 / $28.85 = 41.6 hours of work — about 5.2 days on the clock.
• Invested instead for the 35 years to retirement, that $1,200 grows to $1,200 × (1 + 0.07)³⁵ = $12,812 — 10.68 times the price.

Put together: that $1,200 is 41.6 hours of your life, or $12,812 of retirement money. Neither number says don't buy it — they just put the two hidden costs on the table next to the sticker.

Assumptions and limits

• The hours use take-home pay, so they reflect the time you actually trade for money you keep. Enter gross pay instead and the hours will look smaller than they really are.
• The opportunity cost assumes you would otherwise invest the money and earn the return every year until retirement. That return is not guaranteed — markets swing, and a constant rate is a simplification of a bumpy reality.
• It ignores the utility and joy of the purchase, which are real and legitimate value. A tool you use daily or an experience you will remember can be worth many hours; this only prices the cost side of that trade.
• It treats the price as a one-time lump sum with no contributions. For a recurring cost — a subscription, a habit — multiply by how many times you will pay, or reach for a subscription-style calculator.
• This is arithmetic, not advice. Spending is not bad; the calculator only makes the cost visible so the choice is yours to make with open eyes.

Questions people ask

Why measure a purchase in hours of work?

Because dollars are abstract and hours are not. A price tag says little until you know what you traded for the money behind it — and you paid for it in time, the one resource you cannot earn back. Pricing a purchase in hours of your life turns a vague number into a concrete one: this costs me an afternoon, or this costs me two weeks. That is often the moment the trade becomes obvious in either direction.

Does this mean I should never buy anything?

No. The tool is not an argument against spending — it is an argument for spending consciously. Plenty of purchases are worth many hours of work and the foregone growth: a reliable car that gets you to a job, a tool you use every day, an experience you will carry for years. The point is to see both costs clearly and then decide, rather than letting the sticker price hide what the thing really takes from you.

Why use after-tax income instead of my salary?

Because after-tax pay is the money you actually keep and can actually spend. Taxes, payroll deductions and benefits come out before your check reaches you, so a gross salary overstates your real hourly wage — and a higher wage makes every purchase look like fewer hours than it truly costs. Using take-home pay keeps the hours honest: it is the rate at which you genuinely convert your time into spendable money.

What return should I assume?

A long-run figure of about 5–7% a year is a common starting point for a diversified stock-and-bond portfolio, before inflation. It is an assumption, not a promise — real returns vary year to year and are never guaranteed. If you want a more cautious opportunity cost, use a lower number; if you would have left the money in cash, use a savings rate instead. The lower the return, the smaller the foregone-growth figure.

Does this work for recurring costs like subscriptions?

Not directly — it prices a single, one-time purchase. For something you pay for repeatedly, multiply the hours and the opportunity cost by how many times you will pay, or model the stream of payments with a compound interest calculator treating each payment as a contribution you could have invested. A recurring cost's true price compounds far faster than a one-off, which is exactly why subscriptions add up.