The formula
Buying a prebuilt PC and building one yourself are not two prices — they are two yearly costs over different lifespans. The prebuilt side is the prebuilt PC price divided by the years you expect it to last. The build side is the parts cost plus the value of your build time plus any tools you must buy, divided by the years you expect the build to last. Whichever yearly cost is smaller wins, and the build lifespan where the winner changes is the flip.
Step 1 — Write down the prebuilt and the build
Start with the seven numbers the comparison hangs on. In our worked example the prebuilt PC costs $1,200.00, the prebuilt lifespan is 5 years, the parts cost $900.00, the build time is 6 hours, your hour is worth $25.00, the tools cost $0.00, and the build lifespan is 5 years. Keep them fixed — every later step uses these seven numbers, and changing one halfway through is how comparisons go wrong.
Step 2 — Work out the prebuilt cost per year
The prebuilt cost per year is the prebuilt PC price divided by the years you expect it to last. At $1,200.00 over 5 years the prebuilt cost is $1,200.00 ÷ 5 = $240.00 a year. There is no build time in the prebuilt number, because someone else builds it for you. The buy vs build PC calculator does this for you, and it finds the build lifespan where the winner flips.
Step 3 — Work out what your build time is worth
Your build time is worth the hours spent building times what your hour is worth. At 6 hours and $25.00 an hour the build time is worth 6 × $25.00 = $150.00. This is the step most people skip, and it is the step that changes the answer: $900.00 of parts looks like 25% less than a $1,200.00 prebuilt, but $150.00 of your time closes most of the gap.
Step 4 — Work out the build cost per year
The build cost per year is the parts cost plus your build time’s value plus the tools you must buy, divided by the years you expect the build to last. At $900.00 of parts, $150.00 of build time, and $0.00 of tools over 5 years the build cost is ($900.00 + $150.00 + $0.00) ÷ 5 = $210.00 a year. That is the true cost of building — you pay $900.00 up front, but $150.00 of your time is part of the price, so the build really costs $1,050.00 spread over 5 years.
Step 5 — Compare the yearly costs and find the winner
The prebuilt cost is $240.00 a year and the build cost is $210.00 a year. The gap is $210.00 − $240.00 = −$30.00 — and because the build cost is lower, building wins by $30.00 a year. The rule is simple: a positive gap means buying wins, a negative gap means building wins, and a gap of exactly $0.00 is a tie. The sticker price misleads here — the $900.00 of parts looks like 25% less than the $1,200.00 prebuilt, but the yearly comparison is only $210.00 against $240.00, because your time is part of the build’s price.
Step 6 — Find the build lifespan where the winner flips
The winner depends on the build lifespan, so find the lifespan where it changes. At 4 years of build life the build cost is $1,050.00 ÷ 4 = $262.50 a year against the prebuilt’s $240.00 — buying wins by $22.50 a year — and 4 years is the longest build lifespan where buying still wins. At 5 years the build cost is $210.00 a year — building wins by $30.00 a year — and 5 years is the shortest build lifespan where building wins. The flip happens between 4 and 5 years: if the build lasts 4 years or fewer, buy prebuilt; if it lasts 5 years or more, build it yourself — on these numbers.
What if the build lasts 7 years?
A longer build life flips the answer further toward building. At 7 years the build cost is $1,050.00 ÷ 7 = $150.00 a year against the prebuilt’s $240.00 — building wins by $90.00 a year. The lesson is that the build lifespan matters more than the parts price: a $900.00 build that lasts 7 years is a bargain, and the same build that lasts 1 year costs $1,050.00 a year — buying wins by $810.00 a year.
What if the parts cost $1,100?
More expensive parts flip the answer the other way. At $1,100.00 of parts the build cost is ($1,100.00 + $150.00) ÷ 5 = $250.00 a year against the prebuilt’s $240.00 — buying wins by $10.00 a year. The parts are the number to watch: at $1,050.00 of parts the two tie exactly at $240.00 a year.
The parts cost that ties the two
At $1,050.00 of parts, buying prebuilt and building tie exactly — the build cost is ($1,050.00 + $150.00) ÷ 5 = $240.00 a year, the same as the prebuilt. So the question “is $900.00 a good price for these parts?” has a number attached: $1,050.00 is the line. Below it, build; above it, buy prebuilt — at 5 years, on a $1,200.00 prebuilt with 6 hours of your time at $25.00 an hour.
The prebuilt price that ties the two
At a $1,050.00 prebuilt price, buying prebuilt and building tie exactly — the prebuilt cost is $1,050.00 ÷ 5 = $210.00 a year, the same as the build. So the question “is $1,200.00 a good price for this prebuilt?” also has a number attached: $1,050.00 is the line. Above it, build; below it, buy prebuilt — at 5 years, against $900.00 of parts and 6 hours of your time.
The build time that ties the two
At 12 hours of building, the two tie exactly — the build time is worth 12 × $25.00 = $300.00, so the build cost is ($900.00 + $300.00) ÷ 5 = $240.00 a year, the same as the prebuilt. So the question “how long can I spend building?” has a number attached: 12 hours is the line. Below it, build; above it, buy prebuilt — at $25.00 an hour, on $900.00 of parts over 5 years. At 11.99 hours the build cost is $239.95 a year (building by $0.05); at 12.01 hours it is $240.05 a year (buying by $0.05).
The sticker-price warning
The $900.00 of parts looks like 25% less than the $1,200.00 prebuilt — $900.00 against $1,200.00. If you stop there, building looks like a bargain by $300.00. But 6 hours of your time at $25.00 an hour is $150.00, and that is part of the build’s price, so the yearly comparison is $210.00 against $240.00 — a gap of only $30.00 a year, not $300.00. The sticker price misleads: the honest comparison is the cost per year of ownership. That is why the calculator compares yearly costs instead of sticker prices — and why the build lifespan, not the parts price, is the answer to “buy or build?”