Lead Time Conversion Calculator
Convert lead time into the planning format you need
Use this page when your source data comes in one unit but your operations, planning, or customer commitments rely on another.
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How to Convert Lead Time Between Units
Four steps to translate lead time between hours, days, weeks, and months.
Lead time arrives in whatever unit the person quoting it happens to think in. Suppliers say weeks, project plans say months, MRP systems want days, and service agreements sometimes say hours. Each conversion between them is arithmetic — and each is also a place to import an assumption nobody stated.
The useful discipline is to convert once, on arrival, into a single unit, and to record which working week the original figure assumed. Carrying mixed units through a plan is how a number that was right at the start becomes wrong three handovers later.
Worked example: one lead time, four units, four answers
A supplier quotes "about two months" on a component. Four people in the same business convert that into their own working unit, and none of them does the arithmetic wrong.
- Planner: 2 months as 60 calendar daysRounded month of 3060 days
- Project manager: 2 calendar monthsDepends which months59–62 days
- MRP: 2 months as working days~56–64 calendar days40–46 working days
- Buyer: 2 months as 8 weeksWeeks rounded down56 days
- Spread across the four readingsFrom one quote~8 days
Eight days of spread, and every conversion above is defensible. Months are the culprit: they are the only common lead time unit whose length varies, and rounding them to 30 days or 4 weeks introduces error in opposite directions. If a supplier quotes months, convert to days immediately and write the date down — a date cannot be re-interpreted by the next person to read it.
Lead time unit conversion reference
Working days assume a five-day week with no holidays. Subtract further for every closure in the window, and recalculate entirely if the supplier works six days.
| Quoted | Calendar days | Working days (5-day week) | Working days as elapsed |
|---|---|---|---|
| 1 week | 7 | 5 | ~7 days |
| 2 weeks | 14 | 10 | ~14 days |
| 4 weeks | 28 | 20 | ~28 days |
| 1 month | 28–31 | 20–23 | ~30 days |
| 6 weeks | 42 | 30 | ~42 days |
| 2 months | 59–62 | 40–46 | ~60 days |
| 3 months | 89–92 | 61–66 | ~91 days |
| 12 weeks | 84 | 60 | ~84 days |
| 6 months | 181–184 | 125–131 | ~183 days |
| 1 year | 365 | ~260 | 365 days |
Straight arithmetic. The elapsed column shows what a working-day figure actually costs in calendar time, which is the number a delivery date depends on.
Where conversions introduce error
Four assumptions that ride along with a unit change without anyone deciding them.
Months have no fixed length
The only common lead time unit whose duration varies. Rounding a month to 30 days or to 4 weeks pulls the answer in opposite directions, and February against March differs by three days on its own. Convert months out of a plan at the first opportunity.
The five-day week is an assumption
Working-day conversions assume a five-day week, and plenty of suppliers work six or run continuously. Applying a five-day divisor to a six-day supplier inflates the elapsed time by roughly 17%. Record the working week alongside the number, not just the number.
Holidays only affect one direction
Converting calendar days to working days is unaffected by closures — they are already inside the elapsed time. Converting working days back out to a date is affected by every single one. The same conversion is safe in one direction and lossy in the other.
Converting twice
Weeks to days to months and back rounds at every step, and the errors do not cancel. Convert once into a single unit on arrival, then keep that unit. Better still, convert to a date and pass the date on — dates cannot be re-interpreted downstream.
Related calculators
The Lead Time Conversion Calculator produces an estimate. Real lead times move with supplier capacity, congestion, customs and weather — confirm any committed date with your suppliers and logistics partners before acting on it.
Lead time conversion FAQs
Answers for users converting lead time between different scheduling formats.