Insurance & maintenance estimates
Why I use flat annual figures and how to interpret them.
Published 2026-02-15 · Updated 2026-03-25
Insurance premiums and workshop bills are noisy: they swing with driver history, postcode, vehicle trim, and whether you use a dealer or independent mechanic. CarCostIQ still needs a number for every year in the comparison, so I start from simple annual estimates you can replace.
Why this matters when you buy
Over five years, a $150/year insurance gap becomes $750 — enough to change which vehicle looks cheaper if energy and purchase are close. Maintenance works the same way: steady small differences compound.
How CarCostIQ models it
Each vehicle carries separate annual insurance and maintenance inputs. Defaults come from default assumption values; you override them in advanced fields on the calculator. The same annual figure repeats for each year of the horizon unless you change it mid-scenario by re-running with new numbers.
Real-world caveats
I do not model claim excess, roadside add-ons, or tyre replacement cycles separately. If you know one car runs expensive tyres or has a service pack, fold that into the maintenance field as a rough annual average.
Simple practical example
Suppose the EV is quoted at $1,200/year to insure and the petrol at $950 — that $250 gap becomes $1,250 over five years. If maintenance defaults differ by $200/year, add another $1,000. Either line can exceed a modest annual fuel savings figure for a low-km driver, which is why you should paste real numbers when you have them.
Common misunderstanding
Assuming the cheaper premium car is always cheaper to own. A lower premium might pair with higher fuel use or faster depreciation — TCO still depends on the full stack.
What to override in the calculator
Override insurance for each vehicle as soon as you have quotes. Adjust maintenance upward if you expect big tyres, brakes, or dealer servicing. Leave defaults only when you are still in discovery mode — and re-run after you shop insurers.
Frequently asked questions
- Why flat annual insurance and maintenance?
- Flat figures keep EV vs petrol comparisons fair before you paste real quotes. They avoid hiding different curve shapes that would require much more personal data.
- How should I use the override fields?
- Enter your best estimate of annual insurance and maintenance for each vehicle. Shared result links carry those values so you can revisit the same scenario.
- Do EVs always cost less to maintain here?
- Defaults reflect typical simplified bands, not your workshop. Override if you have a capped-price service plan or expect higher tyre wear.
- What about roadside assistance and glass cover?
- Bundle them into your annual insurance estimate if they matter for your comparison; I do not split sub-cover types.
- Can I compare with month-by-month payments?
- Use annualised totals for insurance. For financed vehicles, use the finance fields for interest while keeping insurance separate.
- Where does maintenance include tyres and brakes?
- In this model it is a single maintenance bucket — increase the annual figure if you expect frequent tyre replacements or major items in the window.
Run the calculator
Apply what you read: pick two vehicles, set your region, then open advanced fields to align insurance, maintenance, residual, and charging mix with your situation.