Lead Time Calculator (order to delivery date)

Understanding the lead time calculator — concept and principle

This calculator adds up the stages between placing an order and receiving the goods, then gives the expected delivery date, the latest date you can order to meet a deadline, and how many spare days you have. Buyers, small manufacturers, online sellers and event planners use it to schedule purchases and avoid stock-outs.

Add every waiting step — with the default inputs: 23 days.

How it is calculated

Total lead time = order processing + production or supplier lead time + shipping and transit + safety buffer (calendar days, rounded to whole days)
Expected delivery date = order date + total lead time
Latest order date = date needed − total lead time
Spare days = date needed − expected delivery date
Lead time in weeks = total lead time ÷ 7

The order date and need date default to today and today + 30 days.

The principle

Lead time is the full span from order to receipt, not just the supplier's production time. Each stage adds to the total: the supplier needs time to process the order, make or pick the goods, and ship them. A safety buffer protects against customs checks, public holidays and delays. Working backwards from the date you need the goods gives the latest order date, which is often the most useful number for planning. Supplier quotes in working days need converting: 5 working days is about 7 calendar days.

Worked example

Defaults: processing 2 days, production 14, shipping 5, buffer 2; order today, need in 30 days.

Total lead time = 2 + 14 + 5 + 2 = 23 days, or 23 ÷ 7 = 3.3 weeks.
For an order placed on Tue, Nov 10, 2026, expected delivery = Thu, Dec 3, 2026.
Latest order date for the need date = Tue, Nov 17, 2026.
Spare days = 30 − 23 = 7: On time.

Because the defaults use today's date, the dates shown move each day; the 23-day lead time and 7 spare days do not.

Each point is the calculator re-run with only “Production or supplier lead time (days)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Production or supplier lead time (days)	Total lead time
3.5	13 days
7	16 days
10.5	20 days
14	23 days
17.5	27 days
21	30 days
28	37 days

How to read the result

Positive spare days mean you can order later or absorb a delay. Zero or negative means the goods will arrive late unless you order now, choose faster shipping or find stock elsewhere. For repeat orders, compare actual lead times with quoted ones and adjust the buffer to match the variation you see.

Common mistakes

Using only the supplier's production time and forgetting processing and shipping.
Mixing working days and calendar days.
Ignoring public holidays at the supplier's location.
Keeping the same buffer for a route that is often delayed.

Keep in mind: The result is only as reliable as the stage estimates. Long or international supply chains vary a lot; confirm dates with your supplier.

Frequently asked questions

What is the difference between lead time and cycle time?

Lead time runs from order to delivery; cycle time is the time to produce one unit once work starts.

How big should the safety buffer be?

Enough to cover the delays you have actually seen on that route; there is no fixed rule.

How do I convert working days to calendar days?

Multiply by about 7 ÷ 5 for a five-day working week, and add public holidays.

Sources: Standard calendar-day arithmetic: lead time = sum of stage durations from order to receipt

Checked 9 Nov 2026. Standard formula: lead time = sum of the stage durations from order to receipt; delivery date = order date + lead time (calendar-day arithmetic).

Your numbers