What is opportunity cost in personal finance?

Opportunity cost is what the money could have done instead. For a big purchase, the most concrete version is its invested future value: 40,000 dollars at a 7 percent annual return becomes about 304,000 dollars in 30 years. The purchase may still be worth it; the point is to decide knowing the number.

Should I use the average or the median wedding cost?

The median is the more honest anchor for a typical couple. The Knot's widely quoted average (34,000 dollars for 2025 weddings) skews high because its survey reaches couples actively planning full weddings, while The Wedding Report's contract-level 2024 median is about 13,195 dollars. Roughly three in four couples spend under 20,000 dollars.

Is investing better than a bigger down payment?

It depends on the gap between your assumed return and your mortgage rate, and on risk. The down payment pays the mortgage rate guaranteed, since interest you never owe cannot be taken back by a bad market. Investing has the higher expected return at 7 percent versus a 6.5 percent mortgage, but it can underperform for years, so a small expected edge often is not worth the risk difference.

Why show the result in today's dollars?

Because 304,000 dollars three decades from now buys far less than it does today. At 2.5 percent inflation, that future balance is worth about 145,000 dollars in today's purchasing power. Many calculators show only the nominal figure, which overstates how the tradeoff will feel when you get there.

Does this account for taxes?

No. The return is before taxes and fees. In a taxable account, dividends and realized gains would trim the growth; in a Roth account, qualified withdrawals would not. The direction of the comparison usually survives taxes, but the margin shrinks, so treat the output as an upper bound for taxable investing.

Opportunity Cost Calculator

See what a big purchase costs in future dollars: the same money invested at your return, in today's dollars too, and against a home down payment.

X f in

Invested future value

$304,490.20

Total you would put in: $40,000.00
Growth on top: $264,490.20
Future value in today's dollars: $145,163.48
Down-payment path (lump sum): $264,574.65
Investing minus down payment: $39,915.56

Invested path vs the down-payment path

Common purchases at your return and horizon

Purchase	Cost today	Future value
Average US wedding (The Knot, 2025 weddings)	$34,000.00	$258,816.67
Median US wedding (The Wedding Report, 2024)	$13,195.00	$100,443.71
New vs used car price gap (KBB, late 2025)	$24,600.00	$187,261.47
Minor kitchen remodel (Cost vs Value, 2025)	$28,458.00	$216,629.55

Quick answer: With the example inputs this page loads by default, the headline result (Invested future value) comes to $304,490.20. See what a big purchase costs in future dollars: the same money invested at your return, in today's dollars too, and against a home down payment. Change any input above and every figure updates instantly in your browser.

Your inputs never leave your browser, and nothing is stored. See our privacy policy .

Fact-check: results on this page are verified against an independently coded reference oracle that covers all 106 calculators on this site. See how we verify .

The real price of a big purchase is what the same money could have become. A 40,000 dollar wedding budget invested at 7 percent grows to about 304,000 dollars in 30 years, worth about 145,000 dollars in today's purchasing power after 2.5 percent inflation. This calculator prices any lump sum or redirected monthly amount the same way, and compares the lump sum against putting it toward a home down payment.

What this result means

The invested future value is the honest price tag of the purchase, in the future dollars you gave up. Two readings keep it fair. First, the today's-dollars figure matters more than the headline number, because decades of inflation shrink what those future dollars buy. Second, the down-payment comparison is a risk contrast, not just a rate contrast: the market return is an assumption that varies year to year, while the down-payment path pays the mortgage rate guaranteed, because interest you never owe is a return no market can take back. Spending the money is not a mistake this tool is judging; it prices the tradeoff so you decide with the number in view.

Assumptions

The invested path grows the lump sum at the effective annual return you set, compounded yearly, and grows the monthly amount as end-of-month contributions at the exact monthly equivalent of that annual rate, so the two views agree.
The return is one constant assumed rate, nominal (before inflation), before taxes, and before fees. Real markets vary year to year; long-run US stock returns near 10 percent nominal include reinvested dividends and shrink to roughly 7 percent after inflation, so treat any single rate as an assumption, not a promise.
The today's-dollars figure divides the nominal future value by (1 + inflation) raised to the number of years. It adjusts only the final value; contributions are not separately indexed.
The down-payment comparison is lump sum only and deliberately simple: a dollar of extra down payment avoids mortgage interest on that dollar, a guaranteed return equal to the mortgage rate, and it is home equity from day one. The comparison compounds the lump at the mortgage rate for the same horizon.
Not modeled in the down-payment path: home price appreciation (it accrues on the whole home whatever your down payment is, so it does not separate the two paths), PMI (a larger down payment that crosses 20 percent of the price also cancels PMI, roughly 0.46 to 1.5 percent of the loan per year per Bankrate, making the down-payment path better than shown), closing costs, and payoff timing.
The preset purchase costs are sourced snapshots: the 34,000 dollar average US wedding (The Knot Real Weddings Study, couples married in 2025), the 13,195 dollar median (The Wedding Report, 2024), a roughly 24,600 dollar new-versus-used car price gap (Kelley Blue Book, late 2025), and a 28,458 dollar minor kitchen remodel (Zonda Cost vs Value, 2025). Refresh them when the sources republish.
This is an estimate for educational purposes only, not financial advice. Spending on things you value is not a mistake; this tool prices the tradeoff so you can choose it deliberately.

Key terms

Definitions for the terms this calculator uses, in our finance glossary .

How it works

The invested future value has two legs. The lump sum grows by compound interest at the effective annual return: future value = amount x (1 + return)^years. The monthly amount grows as an end-of-month annuity at the exact monthly equivalent of that annual rate, rm = (1 + return)^(1/12) - 1, so future value = monthly x ((1 + rm)^months - 1) / rm. Using the exact monthly equivalent keeps the annual and monthly legs on one consistent rate rather than the common shortcut of dividing the annual rate by 12.

The today’s-dollars figure divides the nominal future value by (1 + inflation)^years. The down-payment path compounds the lump sum at the mortgage rate for the same horizon, because a dollar of extra down payment avoids mortgage interest on that dollar, a guaranteed return equal to the mortgage rate. All math runs in decimal arithmetic and rounds only the displayed outputs to the cent.

Worked example

A 40,000 dollar wedding budget, 7 percent annual return, 30 years, 2.5 percent inflation, and a 6.5 percent mortgage rate.

Invested: 40,000 x 1.07^30 = $304,490.20.
In today’s dollars: 304,490.20 / 1.025^30 = $145,163.48.
Down-payment path: 40,000 x 1.065^30 = $264,574.65.
The invested path ends about $39,916 ahead, but that edge is the assumed market return; the down-payment figure is guaranteed by the mortgage contract.

What is included and excluded

The return is nominal, before taxes and fees, and constant; real markets vary year to year. The down-payment comparison excludes home appreciation on purpose: appreciation accrues on the whole home whatever your down payment is, so it does not separate the two paths. PMI is excluded from the math but favors the down payment: putting enough down to reach 20 percent of the price also cancels PMI, which Bankrate puts at roughly 0.46 to 1.5 percent of the loan per year. The preset purchase costs are dated snapshots from the sources below.

Sources

Frequently asked questions

What is opportunity cost in personal finance?: Opportunity cost is what the money could have done instead. For a big purchase, the most concrete version is its invested future value: 40,000 dollars at a 7 percent annual return becomes about 304,000 dollars in 30 years. The purchase may still be worth it; the point is to decide knowing the number.
Should I use the average or the median wedding cost?: The median is the more honest anchor for a typical couple. The Knot's widely quoted average (34,000 dollars for 2025 weddings) skews high because its survey reaches couples actively planning full weddings, while The Wedding Report's contract-level 2024 median is about 13,195 dollars. Roughly three in four couples spend under 20,000 dollars.
Is investing better than a bigger down payment?: It depends on the gap between your assumed return and your mortgage rate, and on risk. The down payment pays the mortgage rate guaranteed, since interest you never owe cannot be taken back by a bad market. Investing has the higher expected return at 7 percent versus a 6.5 percent mortgage, but it can underperform for years, so a small expected edge often is not worth the risk difference.
Why show the result in today's dollars?: Because 304,000 dollars three decades from now buys far less than it does today. At 2.5 percent inflation, that future balance is worth about 145,000 dollars in today's purchasing power. Many calculators show only the nominal figure, which overstates how the tradeoff will feel when you get there.
Does this account for taxes?: No. The return is before taxes and fees. In a taxable account, dividends and realized gains would trim the growth; in a Roth account, qualified withdrawals would not. The direction of the comparison usually survives taxes, but the margin shrinks, so treat the output as an upper bound for taxable investing.

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New to this topic? Our companion guide explains it in plain language: Save Half Your Raise: The Rule That Beats Lifestyle Creep

By Sam Sage Last reviewed July 2026.