How Supplier Count Affects Delivery Time
A batch finishes with its slowest line. What the number of sources does to on-time probability, the legal default on partial shipment, and the order clauses that lock the gain in.
How does the number of suppliers affect delivery time?
A batch is complete only when every line has arrived. Its lead time is therefore not the sum or the average of the line lead times but the longest one, and its probability of arriving on time is the product of the individual probabilities. Five sources that are each 90% reliable produce a batch that is 59% reliable, not 90%.
Consolidating removes that product — but not automatically. Two conditions decide it: the delays have to be independent of each other, and the remaining supplier’s own on-time rate has to be good enough. Where it is not, consolidation lowers delivery reliability.
And the gain is locked in by a written clause. If the supplier collects the lines internally and ships once, the same wait simply moves. Neither side holds a default right here: early performance is the debtor’s option rather than its duty, and a creditor may refuse partial performance — so partial shipment does not exist unless the order says it does.
Three questions hiding inside one
“How does buying from one supplier affect delivery?” looks like a single question. It contains three, and answers to one get used for another:
| Question | What it measures | Does supplier count change it? |
|---|---|---|
| How long does one line take? | Production and transit time of a single item | No. Production time does not shorten because you use fewer suppliers |
| How long does the batch take? | The lead time of the slowest line | Indirectly yes: how many separate durations it depends on changes |
| Will the batch arrive on the promised date? | On-time probability | Directly yes, and very sensitively, because the probabilities multiply |
This page answers the third, because that is the one that hurts. The first is a supplier-selection question, the second a planning question, and only the third improves by cutting the number of suppliers.
The slowest-line rule
The commonest mistake in batch planning is averaging the line lead times. A batch is finished by its last line, not its average one. If two of three lines arrive in three days and one takes fourteen, the batch takes fourteen days — and for those fourteen days the other two sit in your warehouse.
Batch lead time = the maximum of the line lead times
Batch on-time probability = the product of the individual probabilities
The second line is a direct consequence of the first. If the batch was on time then every line was on time, and the probability that several independent things all happen is their product. Reliability does not add up, it multiplies — and numbers below one shrink when multiplied.
How many sources, how reliable a batch?
The 90%, 95% and 98% figures are example assumptions, not a measured industry average.
| Independent sources | Each 90% | Each 95% | Each 98% |
|---|---|---|---|
| 1 | 90.0% | 95.0% | 98.0% |
| 2 | 81.0% | 90.25% | 96.0% |
| 3 | 72.9% | 85.7% | 94.1% |
| 5 | 59.0% | 77.4% | 90.4% |
| 8 | 43.0% | 66.3% | 85.1% |
| 12 | 28.2% | 54.0% | 78.5% |
These figures are the direct output of pⁿ — arithmetic, not measurement — and hold where delays are independent. Read the bottom row: even at 98% source reliability, a twelve-source batch is late more often than one in five. Run it on your own rate with the batch delivery reliability calculator.
The practical reading: there are exactly two ways to raise batch reliability and both are visible in the same row. Either you raise each source’s own rate (move right), or you reduce the number of sources (move up). The second is usually faster, because changing a supplier’s performance takes months while the number of suppliers you use is a decision you can take today.
The independence condition
The product rule has a condition that practice rarely satisfies in full: the delays must be independent. Real delays share causes — the same public holiday, the same customs backlog, the same raw material shortage, sometimes the same sub-manufacturer behind different brands. Where a shared cause exists, sources are late together or on time together.
| Structure of the delays | Batch on-time probability | Delivery gain from consolidating |
|---|---|---|
| Fully independent | The product (pⁿ) — lowest | Highest |
| Partly shared causes | Between the ends | Partial |
| Fully shared cause | The smallest p — highest | Almost none |
The ordering looks backwards: more shared cause means a higher chance of an on-time batch, because all-or-nothing behaviour stops independent risks from stacking. That is not good news — it only means the spread setup is less bad than it looks, and consolidation therefore less good than it looks.
Put last year’s late deliveries on a calendar. Clustered in the same weeks means the shared cause is strong and most of the delivery gain you expect will not arrive; scattered through the year means the independence assumption largely holds and the gain is real. That single hour of work takes the delivery leg of the consolidation decision out of guesswork. Note the condition, though: the claim above holds only while each source’s own on-time rate stays unchanged. A strike or a rule change raises the correlation and lowers every rate — and then the result falls below the independent case.
The product is not the floor
The commonest mistake is to read the product as the worst case. It is only the independent case. The mathematical floor for a joint probability is the Fréchet–Hoeffding lower bound, and it sits far below.
Mathematical floor = max(0, p₁ + p₂ + … + pₙ − (n − 1))
| Sources | Independent (pⁿ) | Mathematical floor |
|---|---|---|
| 2 | 81.0% | 80.0% |
| 5 | 59.0% | 50.0% |
| 8 | 43.0% | 20.0% |
| 12 | 28.2% | 0.0% |
At twelve sources the independent calculation says “28.2% at worst”; the real floor is zero. The independence assumption systematically understates the downside.
Negative dependence comes from shared capacity and is ordinary in supply: one vehicle, one shipping window, one customs slot, one week of production. If a supplier can only finish one of two orders this week, sending one on time delays the other. Each order is individually 90%, yet both arriving is 80%, not 81% — worse than independence, in a setup that looks reassuring because the two are never late together.
One supplier moves risk, it does not remove it
This is the most-skipped part of the argument. If your supplier collects the same lines in parallel from its own sub-sources, your five-source problem becomes its five-source problem. The mathematics does not change; only whose ledger it sits on does.
Three questions separate a transferred risk from a hidden one:
- Is there a written lead-time commitment? Does the supplier commit to the date, or relay whatever its own source tells it? The second is pass-through, not transfer.
- Is there a stock-holding obligation? For items you consume regularly, the supplier holding an agreed buffer is the only mechanism that insulates you from its sub-source delays.
- Does a delay have a consequence? If nothing follows from missing the date, the lead time is a forecast rather than a commitment.
If all three answers are no, going to one supplier gains nothing on the delivery side; it only makes the risk invisible. Invisible risk cannot be managed — in a spread setup you at least know which source is late.
Partial shipment: the clause that locks the gain
Everything above rests on one assumption: that the batch must arrive complete. Remove it and the model changes. With partial shipment allowed, each line arrives on its own date, only the late line is late, and the part of the job that can proceed proceeds. The unit of measurement drops from the batch to the line.
Partial shipment off: batch = its slowest line
Partial shipment on: each line = its own lead time
Under Turkish law neither side holds a default right here, and the reasoning rests on three provisions rather than one — a distinction worth making, because the wrong article is routinely cited.
| Question | Answer | Basis |
|---|---|---|
| Must the supplier send the ready lines early? | No. Early performance is the debtor’s option, not its duty. | Code of Obligations art. 96 — the debtor may perform before the time expires |
| Must the buyer accept partial performance? | No. Where the whole debt is certain and due it may refuse. | Code of Obligations art. 84, “Partial performance” |
| What changes between merchants? | Where the contract is objectively capable of performance in parts, the buyer’s rights are already confined to the undelivered part. | Commercial Code art. 23/1(a), first limb |
The common error is to base “the supplier need not send the ready lines” on art. 84. That article protects the buyer — it stops a supplier imposing partial performance — and by its own wording applies only where the whole debt is “certain and due”, whereas the early-shipment question arises before the delivery date. Article 96 governs that stage.
Article 23/1(a) of the Commercial Code deserves its own note because it has two limbs joined by “or”, and the usual summary keeps only the second. Where the contract is capable of performance in parts given its nature, the parties’ purpose and the kind of goods — no acceptance required — or where it is not but the buyer accepted partial delivery without reservation, the buyer may exercise its rights only in respect of the undelivered part. A multi-line, objectively divisible order already falls in the first limb, so a reservation alone does not preserve everything. The same article preserves termination where the missing part destroys or materially weakens the purpose of the contract — an argument that becomes much harder after an unqualified signature.
What changes by category
The mathematics above is category-independent — bathroom products, electrical materials, personal protective equipment or office consumables all behave the same way. Three things do change by category, and all three are inputs to the same calculation:
| What varies | Effect | Example contrast |
|---|---|---|
| How many separate sources the lines spread across | This is n in the product; the largest effect sits here | A group one manufacturer supplies as a full range versus a group where each line comes from a different brand |
| Whether the lines depend on one another | If they do, partial shipment does not help — the batch still waits | A set installed together versus consumables used independently |
| Stock item or made to order | Stock items show high rates and weak shared causes; made-to-order the reverse | Standard sizes versus custom sizes or custom colours in the same category |
The third row explains why two companies buying from the same category get very different results: the rate is driven not by the category but by which lines you choose within it. Custom sizes and custom colours make a batch markedly more fragile without changing the category at all.
This is also where buying a group from a single manufacturer earns its delivery benefit. If the lines can be chosen from that manufacturer’s own range, n genuinely falls. If the manufacturer buys part of the list in to complete it, n has fallen on paper only — and the only way to find out is to ask: “which of these lines do you manufacture, and which do you source?”
Five lines to put in the order
Delivery reliability is not a supplier attribute; it is an order design problem. These five lines make the whole calculation above actionable:
- Partial shipment is permitted. Without it the supplier has no duty to send ready lines early (art. 96).
- Who pays freight on a partial shipment. Leave it open and the supplier will sensibly wait and send once, which makes the first line worthless.
- The confirmed delivery date and the revision procedure. “About two weeks” is not a lead time; only a written date can be measured.
- The list of critical lines. Which line stops the job? Partial shipment only helps where priority is defined.
- The reservation procedure for incomplete deliveries. Put it in the goods-receipt instruction (Commercial Code art. 23/1(a)).
These five work regardless of supplier count, but they become essential once you consolidate, because in a single-supplier setup one party alone decides whether to hold the batch. Measure the money side of the same decision with the consolidation savings calculator, and the delivery side with the batch delivery reliability calculator. The rest of the consolidation case — cost, negotiation, audit and the arguments against — is on single supplier benefits.
Frequently Asked Questions
How does buying from a single manufacturer affect the delivery schedule?
Because a batch is complete only when every line has arrived, its on-time probability is the product of the individual probabilities. Five sources at 90% each give a 59% batch. Going to one source removes that product and the rate becomes that source’s own. The gain depends on two things: whether the delays were independent of each other, and whether the remaining supplier’s rate is good enough. Where it is not, consolidation lowers delivery reliability.
Is batch lead time the sum of the line lead times?
No, it is the maximum. Lines are procured in parallel, so the batch finishes with its last one. If two of three lines take three days and one takes fourteen, the batch takes fourteen days. Summing or averaging is the commonest planning error and the one that produces the most delay.
Does cutting the supplier count speed up delivery?
It does not shorten the production or transit time of any single line. What it changes is how many separate risks the batch depends on at once, so the gain shows up as reliability rather than speed: the same lead time is missed less often. Your own internal approval time is not part of this and does not change with supplier count.
Can a buyer insist on partial shipment?
Not by default — and the reason is usually attributed to the wrong article. The supplier is under no duty to send the ready lines early because article 96 of the Turkish Code of Obligations makes early performance the debtor’s option: the debtor may perform before the time expires. The buyer in turn cannot be forced to accept partial performance: under article 84 it may refuse where the whole debt is certain and due — but that article protects the buyer rather than limiting what it can ask for, and its “certain and due” condition means it does not reach the early-shipment question at all. Between merchants Commercial Code art. 23/1(a) applies as well. Together they point to one conclusion: put partial shipment in the order, and settle the freight for the extra shipment in the same clause.
What should I do when a delivery arrives incomplete?
Write the missing lines and your reservation on the delivery note. Under article 23/1(a) of the Turkish Commercial Code a buyer that accepted partial delivery without reservation may exercise its rights only for the undelivered part; the same article preserves termination where the missing part destroys or materially weakens the purpose of the contract, but an unqualified signature makes that far harder to argue.
How do I measure my own on-time delivery rate?
List the last 20 orders and record two dates for each: the confirmed delivery date and the actual goods-receipt date. An order is on time if the actual date is not later than the confirmed one. Rate = on-time count ÷ 20 × 100. Where the date was revised mid-order, decide up front which one counts: the first confirmation measures planning quality, the last revision measures only whether the latest promise was kept.
Sources
- Method note — this page uses no benchmark on-time delivery rate. Every percentage here is arithmetic derived from a rate the reader measures; the table values are the direct output of pⁿ, not a measurement. The two results the model rests on are standard probability: the joint probability of independent events is their product, and a joint probability can never exceed the bounded by the Fréchet–Hoeffding limits, max(0, Σp − (n−1)) and min(p) — the product is a point inside that interval, not its floor
- Turkish Code of Obligations (Law no. 6098) art. 84, “Partial performance” — Official Gazette 4 February 2011, no. 27836. Where the whole debt is certain and due, the creditor may refuse partial performance; if the creditor accepts it, the debtor may not withhold the part it has acknowledged. The provision is not mandatory and the parties may agree otherwise
- Turkish Commercial Code (Law no. 6102) art. 23/1(a) — Official Gazette 14 February 2011, no. 27846. Where the buyer accepts partial delivery without reservation, its rights may be exercised only in respect of the undelivered part; termination remains available where the missing part destroys or materially weakens the purpose of the contract
How we choose sources, verify figures and date our pages is set out in how we source and verify what we publish. Spotted an error? Write to info@aksco.com.tr — verified errors are corrected.
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