How to Compare Costs Before Making a Big Purchase
A framework for evaluating any expensive purchase against alternatives — beyond just price tag.
The sticker price is the LEAST useful number when comparing major purchases. Total cost of ownership (TCO) is what matters — and it's often 2–10× the sticker.
What to actually compare
For any purchase over a few months' rent, gather four numbers:
- Upfront cost — the sticker plus delivery, installation, taxes
- Ongoing cost — running, maintenance, subscriptions, insurance, fuel
- End-of-life cost — disposal, replacement timeline
- Opportunity cost — what else this money could have done
The "headline price" is one of four. The other three usually swing decisions.
Example: $30k vs $50k car
Sticker difference: $20,000. Most people stop here. But:
| Cost | $30k car | $50k car |
|---|---|---|
| Sticker | $30,000 | $50,000 |
| Stamp duty / sales tax | ~$1,500 | ~$2,500 |
| Insurance (5 yrs) | ~$5,500 | ~$8,500 |
| Fuel (5 yrs at typical km/yr) | ~$8,000 | ~$8,000 |
| Servicing (5 yrs) | ~$3,500 | ~$5,500 |
| Depreciation (5 yrs) | ~$15,000 | ~$25,000 |
| 5-year TCO | ~$63,500 | ~$99,500 |
Real cost difference: $36,000 — almost double the sticker difference. That's not because the $50k car is bad. It's because most people massively under-budget the ongoing cost.
Example: $1,500 phone every 2 years vs $400 phone every 3 years
- Premium track: $1,500 × 5 phones in 10 years = $7,500
- Budget track: $400 × 3-4 phones in 10 years = $1,500
- 10-year difference: $6,000
Invested at 7%, $6,000 over 10 years becomes ~$10,000. The difference compounds.
This isn't an argument against premium phones (they're great). It's an argument for KNOWING the real cost before committing.
The repair-vs-replace question
For appliances, electronics, cars older than 8 years:
- Repair cost > 50% of replacement cost → usually replace
- Repair cost < 30% of replacement cost → usually repair
- Repair cost 30–50% → consider age, reliability history, your patience
Don't include emotional attachment in this calculation. Run the numbers cold; decide on feelings separately if you must.
The new-vs-used premium
For cars specifically: a 2-year-old car typically costs ~70% of new but has 95% of the remaining useful life. The "new car smell" is a $5,000–$10,000 indulgence.
For electronics: refurbished from manufacturer typically saves 20–35% with same warranty. Use it when available.
How to actually decide between two options
- Define what you need it FOR — the use case, not the features
- List 2–3 viable options at different price points
- Calculate 5-year TCO for each (use rough estimates — exact numbers don't matter, RELATIVE numbers do)
- Compare — divide TCO by years of expected use to get cost-per-year
- Consider — is the more expensive option giving you something worth that delta?
A $1,500/year difference is $125/month. Ask yourself: would I pay $125/month for the extra features? If yes, buy the better one. If no, don't.
The single best money question
For ANY major purchase, ask one question: "If this money were instead invested for 10 years at 7%, what would I have?"
A $40,000 luxury car upgrade vs a $25,000 sensible one = $15,000 difference. Over 10 years at 7%, that's $30,000. Over 20 years, $58,000.
If the upgrade brings you $58,000 worth of joy over 20 years — buy it. If you'd rather have the $58,000 — don't.
The honest answer to that question shapes more big purchases than any budget app.
The bottom line
Comparing only the sticker price is how people end up house-poor, car-poor, and renovation-poor. Total cost of ownership, calculated honestly across the lifetime of the purchase, is the only fair comparison. Five minutes of math at decision time can save tens of thousands over the next decade.