You calculate supplier lead time from your purchase records by counting the calendar days from the date you placed the order to the date the goods were received, then keeping those days per supplier, per route. Supplier lead time tracking is that list, updated when a new receipt lands, and the two figures you actually use are the median and the worst case, because the average hides the rain week inside a number that looks safe. Tally's purchase register gives receipt dates; order dates come from the purchase order if you recorded one, or from the notebook or WhatsApp thread where you placed the call. A Guwahati FMCG owner opens the last six Kolkata oil receipts on Tuesday at 4 PM: 6, 7, 8, 8, 11 and 14 days. Median is 8. Worst case is 14. He writes both against the supplier's name, then uses 8 in the reorder point and 14 as the buffer conversation.
Key Highlights
- Lead time is calendar days from order date to receipt date, counted per supplier and per route, not a feeling of "about a week"
- Keep the median and the worst case from the last handful of receipts; the average pulls a 14-day rain delay down to a 9 that looks safe
- Tally holds the purchase voucher date; the order date lives on the purchase order if you recorded it, or in the notebook where you placed the call
In This Article
- How do I calculate supplier lead time from my purchase records?
- What supplier lead time tracking actually records
- Median and worst case, from six receipts
- Where the two dates live in Tally
- Why "about a week" stocks you out
- Writing lead time next to days of cover
- Frequently Asked Questions
How do I calculate supplier lead time from my purchase records?
Open the last few purchases from that supplier. For each one, write the day you ordered and the day the godown signed the receipt. Subtract. That gap is lead time for that trip. Do it six times. Sort the six numbers. The middle of the list is the median. The largest is the worst case. Those two are how you calculate supplier lead time from your purchase records.
A single trip is a story. Six trips are a supplier. Kolkata oil on 3 June, goods in on 11 June, is 8 days. That 8 does not tell you what to do in July. The list does.
If you never wrote the order date, you still have the receipt. The purchase voucher date is the day stock entered the books. The missing half is the day you asked. That half lives in the WhatsApp chat with the supplier, or in a line the purchase person already keeps: "called 3 June, 20 cases oil." Supplier lead time tracking starts the day you begin pairing those two dates. Until then, lead time is whatever the owner remembers, which is how three suppliers become "about a week."
This number is the one Tally will not store against the stock item. It is also the one the reorder point formula cannot run without. Average daily sales times a guessed week is a guessed purchase.
What supplier lead time tracking actually records
Lead time is days from placing the purchase to goods in the godown. Not days from invoice to payment. Not days the truck spent on the highway after it left. The clock starts when you commit, and it stops when quantity is in your location.
Write four columns, one row per receipt.
| Column | What you write |
|---|---|
| Supplier and route | Kolkata oil, highway; Guwahati local, same-city |
| Order date | Purchase order date, or the day you called |
| Receipt date | Goods receipt or purchase voucher date in Tally |
| Days | Receipt minus order, calendar days |
Route matters. The same company shipping from Delhi in fair weather and from a flooded warehouse in July is two lead times. Split the rows if the origin changes.
MOQ, meaning minimum order quantity, is a different number. A supplier who will not ship under 20 cases changes the purchase quantity, not the days the truck takes. Keep MOQ next to lead time if you want, in a fifth column. Do not let it replace the days.
A notebook with 80 rows for the movers is enough for this sheet. Update a row when the next receipt lands, not in a year-end project. Six recent trips beat forty trips from 2023, because the highway and the supplier's own stocking have both changed.
The purchase report from Tally on mobile is the buy-side list: which supplier, which bills, which value. It tells you who you bought from. Lead time is the extra subtraction you do on the dates behind those bills.
Median and worst case, from six receipts
Tuesday 4 PM. Last six Kolkata oil receipts, already sorted:
6, 7, 8, 8, 11, 14.
Median of six is the average of the two middle numbers, 8 and 8, so 8 days. Worst case is 14.
The arithmetic mean of the same list is (6+7+8+8+11+14) ÷ 6 = 9. 9 looks like a week and a bit. It is also a number that never happened. No truck in this list took 9 days. Two trips took 11 and 14. Those are the trips that empty a godown that was planned on 8.
Use 8 as the lead time in the reorder point. Use 14 to set the buffer conversation: the gap from 8 to 14 is 6 extra days of sales. At 24 bottles a day of 1-litre oil, that is 144 bottles you either hold as buffer or accept as a dry week when the rains come. At ₹185 a bottle, 144 bottles is ₹26,640 of cover, or ₹26,640 of sales you will not bill if you skip it.
Keep both figures. The median is what you plan on. The worst case is what you decide about. Dropping the 14 because "that was the rains" is how the next rains surprise you.
Five receipts: 6, 7, 8, 11, 14. Median is the middle one, 8. Same method. Sort the list and look at the last number.
Do not average in a 2-day Guwahati local supplier with the Kolkata line. Different origin, different row, different median.
Where the two dates live in Tally
Receipt date is the easy one. The purchase voucher, or the goods receipt note if you book one, has a date. That is the day quantity entered the location. Stock Summary will show the inward on that date if you drill the item. The voucher is the source.
Order date is harder, and it is the half most books skip.
If you record purchase orders in Tally, the PO date is the order date. Days from PO to purchase voucher is lead time for that trip. That is the cleanest version of supplier lead time tracking, because both stamps are in the same books.
If you do not record purchase orders, the order date is outside Tally. It is the WhatsApp message, the phone call, or the email. Write it the day you place the order, against the supplier's name, with the item and quantity. When the purchase voucher appears, subtract. After six of those, you have the list.
A purchase bill dated 11 June with no order date attached is a receipt without a start time. You can still see that goods arrived. You cannot see how long you waited. Owners who say "Kolkata is a week" are usually reading memory, not this subtraction.
Past-date Stock Summary is quantity-exact at the current rate on the rupee column. For lead time you want dates, not valuation. The voucher date is the fact.
Godown-wise stock does not compute lead time either. It tells you which location went dry. The supplier notebook tells you how many days that location has to wait.
Why "about a week" stocks you out
Three suppliers, one phrase.
Guwahati local: last six trips 1, 1, 2, 2, 2, 3. Median 2, worst case 3.
Delhi: 6, 7, 8, 8, 9, 11. Median 8, worst case 11.
Kolkata: 6, 7, 8, 8, 11, 14. Median 8, worst case 14.
If the owner treats all three as seven days, the local line is over-bought and the Kolkata line is late by a week on its worst trip. The oil at 24 a day, planned on 7, with 96 on hand, has 4 days of cover. A 14-day Kolkata trip is 10 days dry. Fancy Bazaar does not wait 10 days for mustard oil.
"About a week" also hides season. The 14 sat in last August. Planning September on July's 7-day trips is how monsoon stockouts repeat. When you add a new receipt, look at the month. If the worst cases cluster in one season, that season gets its own worst-case figure.
The cost is specific. ₹185 × 24 bottles × 10 dry days is ₹44,400 unbilled on one SKU, plus the retailers who stopped asking. Supplier lead time tracking exists so that 10 is a number you chose to risk or a number you buffered, not a number that arrived as a surprise on a Friday.
Writing lead time next to days of cover
Lead time is useless as a trophy in a notebook. It has to sit next to days of cover on the same line.
Days of cover is quantity on hand divided by average daily sales. On the oil, 96 ÷ 24 = 4. Lead time median is 8. Cover is already below lead time. The purchase is today, which is the same conclusion the reorder point gave with a 3-day buffer.
Monday 9:10 is the look. Velocity names the movers. Stock Summary names quantity. Item-wise sales names the daily rate. The notebook names median and worst-case lead time. Anything whose cover is at or below median lead time goes on the purchase list. The worst-case figure decides how fat the buffer is.
This is the lead-time half of stockout control for distributors. The sales side comes from live reports. The days come from your own receipts. Tally does not raise a hand when cover crosses lead time. The owner still opens the two numbers.
Update the notebook when a receipt is late, not only when it is on time. The 14-day row is the one that changes the buffer. Ignoring it because you were angry at the supplier that week is how the next 14-day week has no oil.
Saturday's count still has to match Monday's Stock Summary. The eight days still have to be true. Supplier lead time tracking is the habit of writing the second date when the gate opens.
Frequently Asked Questions
Q: How do I calculate supplier lead time from my purchase records?
A: Count calendar days from the date you placed the order to the date the goods were received, for several recent trips from that supplier. Sort those days. Use the median as the lead time you plan on, and the largest number as the worst case you buffer for.
Q: What should supplier lead time tracking include?
A: Supplier name, route, order date, receipt date, and the days between them. Keep a handful of recent trips, not a ten-year archive. Split rows when the origin changes. Minimum order quantity is a separate column if you need it.
Q: Why keep the median and the worst case instead of the average?
A: The average mixes a 6-day trip and a 14-day trip into a 9 that never happened. The median is the typical wait. The worst case is the wait that empties a godown planned on the typical wait.
Q: Where do I find the order date if I do not record purchase orders?
A: In the WhatsApp thread, the call log, or a notebook line from the day you placed the order. The purchase voucher date in Tally is the receipt. Pair the two. After six pairs you have a list.
Q: Does Tally store lead time against each stock item?
A: Tally stores purchase voucher dates and, if you record them, purchase order dates. It does not compute lead time as a field next to the item. The subtraction is the owner's, and it belongs in a notebook next to days of cover.
Q: How many receipts do I need before the number is usable?
A: Six recent trips from the same supplier and route is enough to see a median and a worst case. One trip is a story. Forty trips from three years ago is a different highway.
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