How to use the diy vs shop car repair calculator
- Enter the shop's price for the whole repair and the cost of the parts you would buy yourself.
- Enter the cost of tools you do not own and how many repairs you expect to use them for.
- Enter the hours the job takes you, what an hour of your time is worth to you, and an allowance for mistakes as a share of the shop price.
- Read the saving per repair, the break-even number of repairs for the tools and the table of totals after several jobs.
Formula
doing it yourself = parts + tools / repairs they serve + hours x value of an hour + allowance % x shop price
saving per repair = shop price - doing it yourself
break-even repairs = tool cost / (shop price - parts - time - allowance)
The break-even is the number of repairs after which the tools have paid for themselves. If the margin per repair before tools is zero or less, the tools never pay off.
A brake job quoted at $620
Parts cost $240, tools $180 spread over 4 repairs ($45 each), the job takes 5 hours valued at $20 ($100) and the allowance for mistakes is 10% of $620 ($62). Doing it yourself costs 240 + 45 + 100 + 62 = $447, so you save $173 per repair.
Before tools, each repair saves $620 - $240 - $100 - $62 = $218, so the $180 of tools is covered after 180 / 218 = 0.83 repairs. After one repair the shop would cost $620 and doing it yourself $582, a saving of $38; after four repairs $2,480 against $1,788, a saving of $692.
Putting a price on your time and risk
Your time is worth different amounts to different people. Use what you could otherwise earn, or what you would pay to avoid the work, or 0 if the time is free and you enjoy it. The allowance for mistakes stands for a part ordered twice, a tow, or a second visit to a shop to fix what went wrong. It is a guess, so try a few values and see whether the answer changes.
The cost of the car itself matters too. See the Total Cost of Car Ownership Calculator, print a Car Maintenance Schedule to plan jobs, and for a one-off tool use the Tool Rental vs Buy Calculator.
Safety comes first
Brakes, steering, airbags and fuel systems affect your safety and that of others. If you are not sure you can do the job correctly, with the right tools and a safe way to hold the car up, the shop is the safer choice whatever the numbers say. A warranty, a proper diagnosis and a second pair of trained eyes have value that this page does not count.
Assumptions and limits
- The shop price covers the same work as your repair, parts and labor included.
- Tools are used up evenly across the repairs you give and never wear out or lose value.
- The totals table repeats the same repair and buys the tools once.
- Time is valued at a flat rate per hour and the allowance is a flat share of the shop price.
- The figures are examples for you to replace, not estimates of what any repair costs.
Frequently asked questions
What should I enter for an hour of my time?
Whatever it is worth to you. If you would be earning that hour, use your wage. If you would only be watching television, a low number or zero is fair.
Why is there an allowance for mistakes?
Even careful people sometimes buy the wrong part or need a second try. The allowance keeps the comparison honest.
What does Never at these figures mean?
Parts, time and the allowance cost as much as the shop price, so doing it yourself saves nothing and the tools can never be paid back.
Does the page cover rented tools?
You can enter the rental as the tool cost with 1 repair. For a longer comparison, use the tool rental calculator.