Weeks to Days Lead Time Calculator
Convert lead time from weeks into a usable day count
Use this page when you need to bridge the gap between supplier language and internal scheduling, especially for procurement and production planning.
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How to Convert Weeks to Days
Four steps to quickly translate weekly lead-time quotes into day-based planning.
Converting weeks to days looks like arithmetic and is really a question about definitions. Multiply by seven and you have calendar days. Multiply by five and you have working days. Both are correct answers to different questions, and the person who quoted you "six weeks" usually did not say which one they meant.
This matters more than the multiplication suggests. On a twelve-week quote the two readings sit 24 days apart before any holiday is counted — more than three weeks of difference hiding inside a number everyone thought was agreed.
Worked example: what "12 weeks" costs you if you guess wrong
A supplier quotes 12 weeks on a component. The order goes in on Monday 5 January 2027. Two people read the same quote differently, and neither is doing the arithmetic wrong.
- Read as 12 calendar weeks12 × 7 — the supplier's usual meaning84 days
- Read as 12 working weeks12 × 5 — the planner's usual meaning60 working days
- 60 working days as elapsed timeCoincidentally similar, if no holidays~84 days
- With 4 holidays inside the windowWorking-week reading extends~90 days
- Difference at the delivery dateOn a date that was thought agreed6+ days
Twelve calendar weeks and twelve working weeks happen to land close together when nothing interrupts them, which is exactly why this error survives. Add holidays, or a quote given in working weeks by a supplier who works six days, and the readings separate fast. The fix costs one question: "is that calendar weeks or working weeks?" — asked before the number goes into a plan, not after the delivery is late.
Weeks to days conversion reference
Calendar days assume seven-day weeks. Working days assume a five-day week with no holidays — subtract further for every closure inside the window.
| Quoted | Calendar days | Working days | Working weeks as elapsed time |
|---|---|---|---|
| 1 week | 7 days | 5 days | ~7 days |
| 2 weeks | 14 days | 10 days | ~14 days |
| 3 weeks | 21 days | 15 days | ~21 days |
| 4 weeks | 28 days | 20 days | ~28 days |
| 6 weeks | 42 days | 30 days | ~42 days |
| 8 weeks | 56 days | 40 days | ~56 days |
| 10 weeks | 70 days | 50 days | ~70 days |
| 12 weeks | 84 days | 60 days | ~84 days |
| 16 weeks | 112 days | 80 days | ~112 days |
| 20 weeks | 140 days | 100 days | ~140 days |
| 26 weeks | 182 days | 130 days | ~182 days |
| 52 weeks | 364 days | 260 days | ~364 days |
Straight arithmetic, shown so the two readings can be compared at a glance. The elapsed-time column is what a working-week quote actually costs in calendar terms, which is the number a delivery date depends on.
Why the conversion goes wrong
Four things that break a weeks-to-days conversion, none of which are arithmetic errors.
Nobody states which kind of week they mean
Suppliers usually quote calendar weeks because that is what their production schedule runs on. Internal planners usually think in working weeks because that is what their capacity runs on. The word "weeks" carries both meanings and flags neither, so the mismatch survives every handover until the delivery date arrives.
Holidays only affect one of the two readings
A calendar-week quote absorbs holidays — they are already inside the elapsed time. A working-week quote does not, so every closure extends it. This is why the two readings sit close together on a quiet quarter and drift apart across a period containing a shutdown.
Six-day and seven-day working weeks
A five-day week is an assumption, not a fact. Suppliers running six days convert at six, and continuous-process plants at seven. Applying a five-day assumption to a six-day supplier overstates the elapsed time by roughly 17%, which on a 20-week quote is more than three weeks of phantom delay.
Converting to a count instead of a date
Turning weeks into a number of days is only half the job. The number still has to be applied to a start date with weekends and closures handled, or it will regularly produce a delivery date that falls on a day nobody works. A count is not a commitment; a date is.
Related calculators
The Weeks to Days Lead Time 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.
Weeks-to-days lead time FAQs
Questions about converting weekly lead-time promises into daily planning decisions.