Fixed vs variable ownership cost
Loan
Insurance
Fuel
Depreciation
Other
Scenario comparison
Lean
Realistic
High cost
Ownership scenario table
| Scenario | Monthly cost | Yearly cost | % of income | Difference vs realistic |
|---|
Affordability gauge
| Income share | Meaning | Signal |
|---|---|---|
| < 10% | Car cost is not dominating monthly finances | Wealth builder |
| 10% to 15% | Manageable but should be watched closely | Standard |
| > 15% | Car is starting to behave like lifestyle inflation | Risk |
How this car ownership calculator works
This calculator measures total cost of ownership, not just the loan payment. It combines finance cost, insurance, fuel, maintenance, repairs, parking, tax and depreciation, then tests that total against the 20/4/10 rule. It also adds a future wealth layer by showing what the monthly ownership cost could become if invested instead.
The aim is to show whether the car fits the budget, how much of income it consumes, and how much future value is being given up for the ownership choice.
Core formulas
Loan payment = P × r(1+r)^n / [(1+r)^n − 1]
Monthly depreciation = (purchase price − resale value) / hold months
Total monthly car cost = loan + insurance + fuel + maintenance + repairs + parking + tax + depreciation
Cost per distance unit = monthly total / monthly distance
Opportunity future value = monthly cost invested monthly at chosen return rate
Monthly depreciation = (purchase price − resale value) / hold months
Total monthly car cost = loan + insurance + fuel + maintenance + repairs + parking + tax + depreciation
Cost per distance unit = monthly total / monthly distance
Opportunity future value = monthly cost invested monthly at chosen return rate
The 20/4/10 rule means 20% down payment, loan term of 4 years or less, and all car-related costs staying within 10% of gross income. This page uses your entered gross income as the affordability anchor.
Why opportunity cost matters
Most car calculators stop at cash cost. That misses what the same money could become if it were invested over time. The opportunity cost layer is what turns this from a payment calculator into a true financial decision tool.
Frequently Asked Questions
What is the 20/4/10 rule?+
It is a common affordability guideline that suggests putting 20% down, financing for no more than 4 years, and keeping all car-related costs within 10% of gross income.
Why include depreciation?+
Because depreciation is a real ownership cost. Even if it is not paid out in cash monthly, the car is losing value over time and that affects total cost of ownership.
What counts as total monthly car cost?+
This page includes finance cost, depreciation, fuel or charging, insurance, maintenance, repairs, parking and taxes or registration. That gives a more realistic monthly ownership number than loan payment alone.
Why compare this to grocery budget and savings?+
Because substitution framing makes the decision easier to understand. A car that costs as much as a major household expense may be crowding out other priorities more than it appears.
Is higher car cost always bad?+
Not always. A more expensive car may be justified by safety, work needs or reliability. The key question is whether the cost fits income and still leaves enough room for savings and other core goals.
How accurate is the opportunity cost estimate?+
It is an estimate based on a constant return assumption. Real market outcomes vary, but the calculation is still useful for showing the long-term trade-off of recurring car cost.
