Big Purchase Real Cost Calculator — Rex's Toolbox

Rex says

Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.

Try a scenario

Click to load — tweak from there.

Inputs

Purchase price($)

Paid in cash up front($)

Financing APR on the remainder(%)

Financing term(months)

Running costs($/yr)

Insurance, maintenance, storage, fees

Years you'll own it(years)

Resale value at the end($)

Return the cash would have earned(%)

Result

True lifetime cost

$17,354

Cost per month of ownership

$241

Interest paid on financing

$1,279

Running costs over the period

$5,400

Lost return on cash deployed

$1,674

Monthly finance payment

$258

True cost as a multiple of price

Psst — share this and help Rex grow

One click, a permanent link with your numbers baked in.

More financial

Got your number — what next?

Pick one, it takes 20 seconds

Ask Rex about this resultRex reads your numbers and suggests the next move.Car Buy vs Lease Cost CalculatorCompare the true cost per month of financing a car against leasing the same vehicle.Subscription Audit CalculatorTotal your recurring charges and see what cancelling the unused ones is worth.Sinking Fund Monthly Contribution CalculatorWork out the monthly set-aside for a known future expense so it never hits credit.

How to use this

1Enter purchase price ($).
2Enter paid in cash up front ($).
3Enter financing apr on the remainder (%).
4Enter financing term (months).
5Enter running costs ($/yr) — Insurance, maintenance, storage, fees.
6Enter years you'll own it (years).
7Enter resale value at the end ($).
8Enter return the cash would have earned (%).
9Read your true lifetime cost on the right — it updates as you type.
10Hit Share to keep the scenario or send it to someone.

About this calculator

A sticker price is the smallest part of a large purchase. Financing adds interest, ownership adds recurring costs, and the cash spent stops earning. This calculator totals all four components across the years you expect to own the item — purchase, financing, running costs, and the opportunity cost of the money — then subtracts any resale value to produce a true cost and a cost per month of use. It is deliberately uncomfortable arithmetic, and it is the reason a purchase that feels affordable monthly can still be an expensive decision.

FormulaTrue cost = price + financing interest + (running costs × years) + opportunity cost of cash deployed − resale value. Cost per month = true cost ÷ (years × 12).

Worked example

Using the values the calculator loads with:

Inputs

Purchase price: 12000 $
Paid in cash up front: 4000 $
Financing APR on the remainder: 9.9 %
Financing term: 36 months
Running costs: 900 $/yr
Years you'll own it: 6 years
Resale value at the end: 3000 $
Return the cash would have earned: 6 %

Results

True lifetime cost: $17,353.51
Cost per month of ownership: $241.02
Interest paid on financing: $1,279.43
Running costs over the period: $5,400.00
Lost return on cash deployed: $1,674.08
Monthly finance payment: $257.76
True cost as a multiple of price: 1.45

What each field means

Inputs

Purchase price ($): The purchase price used in the calculation, measured in $. Starts at 12000 $ so you have a working example on load.
Paid in cash up front ($): The paid in cash up front used in the calculation, measured in $. Starts at 4000 $ so you have a working example on load.
Financing APR on the remainder (%): The financing apr on the remainder used in the calculation, measured in %. Starts at 9.9 % so you have a working example on load.
Financing term (months): The financing term used in the calculation, measured in months. Starts at 36 months so you have a working example on load.
Running costs ($/yr): Insurance, maintenance, storage, fees
Years you'll own it (years): The years you'll own it used in the calculation, measured in years. Starts at 6 years so you have a working example on load.
Resale value at the end ($): The resale value at the end used in the calculation, measured in $. Starts at 3000 $ so you have a working example on load.
Return the cash would have earned (%): The return the cash would have earned used in the calculation, measured in %. Starts at 6 % so you have a working example on load.

Results

True lifetime cost: Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Cost per month of ownership: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Interest paid on financing: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Running costs over the period: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Lost return on cash deployed: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Monthly finance payment: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
True cost as a multiple of price: Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

Is opportunity cost a real cost?

It is real in the sense that the money had an alternative use — but only if you would genuinely have invested it. If the cash would have sat in checking, set the return input to your savings rate instead so the figure stays honest.

Why does 0% financing still show a cost?

Because financing interest is only one of four components. Even at 0% you carry running costs, depreciation captured through the resale figure, and, if you also paid cash up front, the return that cash is no longer earning.

How should I estimate resale value?

Look up actual completed sales for the same item at the age you plan to sell, not asking prices. For most consumer goods the honest answer is close to zero after a few years; vehicles, tools, and some instruments are the notable exceptions.

How do I use the cost per month?

Compare it against renting, subscribing, or simply not owning. If a boat costs several hundred dollars per month of ownership and you use it six weekends a year, the per-use cost makes the alternative obvious in a way the sticker price never does.

Accuracy and limitations

Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.

Related tools

Car Buy vs Lease Cost Calculator

Compare the true cost per month of financing a car against leasing the same vehicle.

Subscription Audit Calculator

Total your recurring charges and see what cancelling the unused ones is worth.

Sinking Fund Monthly Contribution Calculator

Work out the monthly set-aside for a known future expense so it never hits credit.

Cite this calculator

Writing about this topic? Grab a citation — every link helps keep these tools free.

APA

RevenueLab. (2026). Big Purchase Real Cost Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/big-purchase-real-cost

HTML

<p>Source: <a href="https://www.revenuelab.fyi/toolbox/big-purchase-real-cost" target="_blank" rel="noopener">Big Purchase Real Cost Calculator — RevenueLab</a> (2026).</p>

Markdown

Source: [Big Purchase Real Cost Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/big-purchase-real-cost) (2026).