Time value of purchases — the half the receipt omits
A receipt records one of the two things you spent.
The money is on the receipt. The decade it was going to spend growing is not. Price your own purchase, then
see why the receipt is not the cost.
$1,200.00
The number everyone agrees on, and the only one anyone checks.
$2,360.58
The same money at 7% after inflation, in today’s money.
What is this purchase really costing you?
This is not a tool for talking you out of things. It prices the alternative, and you decide. If the purchase is worth it to you, it is worth it.
The free version covers one-time and monthly purchases up to 10 years. Pro adds the full 50-year horizon, weekly and annual purchases, your own inflation and fee assumptions, image and CSV export, and a shareable link. Opening a link someone shares with you is free.
Pro is a separate one-time purchase. If you already subscribe to DCA Simulator Pro, this is not included in it — worth knowing before you click, rather than at the checkout.
Educational content only — not financial advice. Past returns are past returns; nothing here is a projection of any specific asset, or a recommendation to buy or not buy anything.
A receipt records one of the two things you spent.
It records the money. It does not record the decade that money was going to spend growing, or the fact that the object you swapped it for is on a curve heading the other way.
You hand over an amount. The receipt says that amount. Everyone agrees on it, and it is the only number anyone ever checks.
That money had a second future: invested and left alone. That future keeps compounding whether or not you think about it.
You were already saving toward something. That money was going to arrive there too, and now it arrives later.
Take the phone in the panel above. Twelve hundred dollars, once, ten years ago.
The money would be worth $2,360.58 today, in today’s money, at seven percent after inflation. You paid $1,200 to not have it, so the forgone part is $1,160.58 — near enough the price of the phone all over again, and a number that appears on no receipt, no statement and no budget.
Then the part that actually changes a decision. Against a $100,000 target funded at $500 a month, that plan arrives in 149 months on its own and in 146 with the $1,200 redirected into it. The phone cost three months.
This is not an argument for never buying a phone. You needed a phone. It is an argument that the number you used to decide — $1,200 — was not the number that mattered, and you had no practical way to compute the one that did.
The reason nobody does this by hand is that doing it properly means converting a real return to a nominal one, compounding on the right cadence, deflating the result back to today’s money, and then running your whole savings plan twice to see what moved. It is four steps of arithmetic with a trap in each one.
Nobody skips this because they do not care. They skip it because it is genuinely fiddly.
Nothing here is hidden. Check every step.
These are the three purchases from the top of the page, with the working shown. If a number here disagreed with the calculator below, the calculator would be wrong — so they are produced by the same engine.
The field says seven percent after inflation. Compounding needs a nominal rate, so it converts first: (1.07 × 1.03) − 1 = 10.21%
Ten years at 10.21% nominal, one contribution at the start and nothing after it. 1.102110
Deflate by ten years of 3% inflation, so the answer is in money you recognise: ÷ 1.0310
Not a formula. The same calculation run twice — your plan alone, then your plan with the purchase in it. The difference is the months.
● Engine output, free settings
| Purchase | Paid | Money today | Forgone | Delay |
|---|---|---|---|---|
| Car upgrade | $18,000.00 | $35,408.72 | $17,408.72 | 40 months |
| Phone upgrade | $1,200.00 | $2,360.58 | $1,160.58 | 3 months |
| Watch | $450.00 | $885.22 | $435.22 | 1 month |
| Total | $19,650.00 | $38,654.52 | $19,004.52 | 43 months |
Every money figure is in today’s money. “Forgone” is what the money would have become minus what you paid — the part of the decision that never appears on a statement. The delay is measured against a $100,000 target funded at $500 a month, which reaches it in 149 months on its own; both of those are fields, and both are free.
The delays do not add. Forty, three and one make forty-four, but run together the answer is forty-three. Each one is a whole-month answer to a separate question, so run several purchases together rather than summing them.
The watch is the interesting row. Four hundred and fifty dollars is the kind of number that does not feel like a financial decision at all — and over ten years it is a four-hundred-and-thirty-five-dollar one, and a month. Not ruinous. Just bigger than it looked, which is the only claim this tool makes.
Run the same three at a lower return, or against your own target and your own monthly contribution, and the answers move. That is the point of putting the controls in your hands rather than printing a scary number and asking you to believe it.
The tool is not trying to talk you out of the car. It is trying to make the second number visible while you can still act on it.
Four fields. No account, no email, no upload.
There is no signup and nothing to attach your figures to. They are sent to this site to be calculated and are never written to a database, kept after the answer comes back, or passed to anyone else.
Enter the purchase
What you paid, and whether it was a one-off or a monthly commitment. A number and a dropdown.
Set the horizon
How far forward to run it. The default is ten years, which is long enough to matter and short enough to still be your life.
Add your goal, if you have one
A target and what you already put in each month. Both optional. This is the part other calculators skip.
Read the two answers
What that money would have become, and how many months later the purchase made you arrive.
The default rate is seven percent after inflation. That is a deliberate, disclosed round-up: the measured real figure over 1928–2025 is 6.74%, and the inflation default of 3% is a round-down of 3.07%. Both roundings are stated in the tool rather than buried, because a calculator that quietly flatters its own output is worse than no calculator.
You can change the rate. You should — run it at four percent and see whether your conclusion survives. A number that only works at the optimistic setting was never a conclusion, it was a hope.
Most complaints about this tool are correct.
Here are the four that come up, answered honestly rather than deflected. If one of them is a dealbreaker for you, it should be.
“By this logic you never buy anything.”
That is a real failure mode, and it is a bad way to live. Every purchase has a forgone-growth number attached, including the ones that are obviously worth it — a bed, a decent coat, a holiday you still remember.
The tool does not say the number is too big. It says here is the number. Deciding it was worth paying is a perfectly good outcome, and it is a better one than not knowing.
“Seven percent is not guaranteed.”
Correct. It is not a promise, it is an assumption, and it is the one doing the most work on the page — which is exactly why it sits in an editable field rather than in the fine print.
The measured real figure over 1928–2025 is 6.74%; the default rounds it up to 7% and rounds inflation down, and the tool says so. Run it at four percent. If the conclusion flips, it was never robust.
“The goal and the monthly amount are your numbers, not mine.”
They are, and the months are entirely hostage to them — which is why both are fields. Put your own target and your own monthly contribution in and the delay moves with them.
If you are not saving toward anything specific yet, the tool leaves that line blank rather than inventing a goal for you. A delay is a comparison between two paths, and with no existing path there is nothing to compare. The forgone figure still stands on its own.
“This is just guilt with a chart on it.”
It would be, if it only ever ran backwards over things you already own. Used that way it is archaeology, and archaeology has no decision in it.
It earns its keep before the purchase, on the thing you are still deciding about — where the number is an input rather than a verdict. Past purchases are for calibration, not for self-flagellation.
Built for people who already run the numbers.
This is a calibration instrument, not a budgeting app and not a lecture. It suits a particular kind of person and is genuinely useless to everyone else.
- You are weighing a specific purchase right now and want the forgone-growth figure before you commit, not after.
- You think structurally — you want the mechanism exposed, and you will change the assumptions to test whether a conclusion holds.
- You are comfortable being told a number you will then overrule on purpose, because some things are worth paying for.
- You already invest, so “the money would have been invested instead” describes what you would actually have done with it.
- You want to be told what to buy. It has no opinion and offers no recommendation.
- You are looking for a budgeting system, spending categories, or bank-account syncing. It does none of that and never will.
- You need certainty. Every figure rests on an assumed rate of return, and that assumption is visible and editable precisely because it is not certain.
- Seeing the cost of past purchases would send you into a spiral rather than into better decisions. That is a real reaction and the tool will not help it.
If none of that is you, close the tab — no hard feelings. A tool you were never going to act on is worse than no tool, because it costs you the ten minutes and leaves you feeling like you did something.
What the true cost of a purchase calculator is telling you.
Answered against what the tool actually does, not against what would be convenient to claim.
What does a purchase actually cost?
The price on the receipt, plus everything that money would have become had it stayed invested. Those are two different numbers and only one of them shows up on your statement. The receipt is what you paid. The second figure is what you gave up.
This is not a trick of arithmetic, it is just compounding read in the other direction. Money spent at 30 is not the same size as money spent at 55, because the earlier money had more time to work. The tool prices that difference so you can see it before you decide, rather than reconstructing it afterwards.
Does this mean I should never buy anything?
No. A tool that answers “do not buy it” to every input is not a tool, it is a mood. Money exists to be spent at some point, and a purchase that makes your life materially better is doing its job.
What this changes is which purchases you make deliberately. Most people have a small number of recurring or large purchases that would not survive being priced properly, and a much larger number that would survive easily. The point is to find the first group, not to feel guilty about the second. If the number comes back and you still want the thing, buy it — you now know what it costs.
How do you calculate what a purchase would have been worth?
You compound the amount forward at an assumed return for the number of years you choose. The default is 7% real — that is, after inflation, rounded up from a measured 6.74%: the S&P 500 with dividends reinvested returned 10.02% a year geometric over the 98 years from 1928 to 2025 (A. Damodaran, NYU Stern), against CPI-U inflation averaging 3.07% over the same window (US Bureau of Labor Statistics). (1.1002 / 1.0307) - 1 = 6.74%.
It is a rounded figure and not “the historical average”. It is also an assumption about the future dressed as a measurement of the past, which is the honest way to describe every return input in every calculator of this kind. Lower it and watch the answer move.
Are the results in today’s money?
Yes. Because the return is a real rate — already net of the 3% default inflation — the figure the tool shows you is in today’s purchasing power, not in inflated future dollars.
This is worth being deliberate about, because it is where most back-of-envelope versions of this calculation go wrong. Compounding at a nominal 10% and then quoting the result as though it were spendable today overstates the answer by roughly a third over ten years. Do not deflate the result yourself as well, or you will subtract inflation twice.
What does the free version cover?
One-time and monthly purchases, over a horizon of up to ten years. Opening a result link someone shares with you is free for anyone, always, with no account.
Pro adds the fifty-year horizon, weekly and annual purchases, your own inflation and fee assumptions, and image and CSV export. Note that fees default to zero in the free version, so the figure you see is gross of any platform or fund cost — a real portfolio pays something, and it comes off the number.
Is my data saved or sent anywhere?
No. There is no account, no email gate and no sign-up. Your figures are sent to this site to be calculated, and the answer comes straight back — nothing you enter is written to a database, kept after the response, or passed to any third party.
The only thing this page stores in your browser is whether you chose dark mode. The shareable result link carries only the assumptions you chose.
Everything above stays free. Pro goes further.
Pro adds the full fifty-year horizon, weekly and annual purchases, your own inflation and fee assumptions, and image and CSV export.
Paid once. Not a subscription, not a bundle.
The free version covers one-time and monthly purchases up to ten years, and opening a link someone shares with you is free. If that already told you what you needed, you do not need this. Educational content only — not financial advice.