What is a back-to-back letter of credit, and why must the two credits mirror?

By Saurabh Goyal, Founder & CEO of Phlo Systems. Published 24 July 2026.

The classic middle-trader structure: you sell to your buyer under one letter of credit, and you use that sale to support a second credit issued in favour of your supplier. Two credits, one cargo. It lets a trader run volumes far beyond its balance sheet, which is why the structure is everywhere in commodity trading. It also contains a trap that shows up nowhere on either credit individually: the two credits must be satisfiable by the same shipment and, for most documents, the same paper. Where they diverge, the middle trader is the one holding the difference.

The 30-second answer: in a back-to-back structure, the incoming credit (your purchase side obligations to your supplier) must sit strictly inside the outgoing credit (your sale side entitlements from your buyer) at every point: dates, amounts, tolerances, description, documents. Any term where the purchase credit is looser than the sale credit allows your supplier to perform in a way you cannot pass through, and the shortfall lands on you, at cargo scale, not fee scale.

The mirror, term by term

Term	The rule for the middle trader	What the gap costs if you get it wrong
Latest shipment date (44C)	Purchase credit's date must be on or before the sale credit's	Supplier ships legally under your purchase credit, and you are already late under your sale credit
Expiry and presentation period (31D, 48)	You need room to receive documents on the purchase side, then re-present on the sale side	Documents arrive compliant but too late to pass through
Quantity and tolerance (39A)	Purchase tolerance must fit inside sale tolerance	Supplier loads 9,800 tonnes against a purchase credit allowing 10 percent; your sale credit allows 5 percent; the difference is yours to settle
Goods description (45A)	Purchase description must satisfy the sale description word for word where documents pass through	An invoice you cannot reuse, and a spec dispute at the port of discharge
Documents (46A)	Every document the sale credit demands must be obtainable from the purchase side, from an issuer both credits accept	A missing certificate that no one can now issue, because the goods have sailed
Ports and routing (44E, 44F)	Load and discharge ports must be consistent across both credits	A bill of lading that is compliant on one side and discrepant on the other
Inspection	The inspector named on the sale side must be the one who actually attends loading	Quality is final at loading; the certificate that exists is not the certificate the sale credit names

Two of these deserve special attention because they are irreversible. The shipment date: if your purchase credit lets the supplier ship later than your sale credit permits, there is a window in which the supplier is compliant and you are already in breach, and the supplier has no reason to care. And inspection: on most bulk terms, quality and weight are determined at loading. If the sale credit calls for a certificate from a named independent inspector and your purchase credit accepts the supplier's own certificate, the moment loading completes without your inspector present, the discrepancy on your sale side is permanent.

Why this fails in practice

Nobody drafts a back-to-back mismatch on purpose. The two credits are negotiated at different times, with different counterparties, often by different people. The sale credit is amended and the purchase credit is not. A tolerance is granted to the supplier in a phone call and formalised in an MT707, and no one re-runs the comparison. Each credit, read alone, looks fine; the defect exists only between them. That is what makes it dangerous: standard document checking, which examines one presentation against one credit, will never see it. The comparison of credit against credit is a separate discipline, and it has to re-run every time either side is amended.

The same logic applies, in softer form, to any trader with a purchase contract on one side and a sale credit on the other. The credit you have received is only workable if the contract you have signed upstream can produce the shipment and the documents it demands. The workability review is the one-credit case; the mirror check is the two-credit case; the discipline is the same.

Back-to-back is not transferable

The two structures are often confused. Under a transferable credit, one credit exists and the first beneficiary transfers part of it to a second beneficiary; UCP 600 article 38 governs what may change on transfer (amount, unit price, expiry, presentation period and latest shipment date may be reduced or curtailed, insurance cover increased). The bank machinery keeps the two halves aligned. Under back-to-back, there are two independent credits from two independent issuing banks. No article of UCP 600 links them. Nothing keeps them aligned except the middle trader's own diligence, which is precisely why the mirror discipline exists.

Frequently Asked Questions

What is a back-to-back letter of credit?

A structure in which a trader uses the credit received from its buyer to support a second, independent credit issued in favour of its supplier. Two separate credits from separate banks cover one underlying cargo, letting the middle trader finance transactions beyond its own balance sheet.

What is the difference between a back-to-back and a transferable letter of credit?

A transferable credit is one credit, partially transferred to a second beneficiary under UCP 600 article 38, with the bank controlling what changes on transfer. Back-to-back involves two independent credits with no legal link between them. The alignment that article 38 enforces automatically for transfers must be engineered by hand in a back-to-back structure.

Which terms must be tighter on the purchase credit than the sale credit?

The latest shipment date must be no later; the quantity tolerance must fit inside the sale side's tolerance; the goods description must satisfy the sale credit's wording; every document the sale credit requires must be obtainable under the purchase credit from an acceptable issuer; and the timeline must leave room to receive documents on one side and re-present them on the other before expiry.

Why do banks dislike back-to-back letters of credit?

Because the issuing bank on the purchase side is exposed to a trader whose ability to pay depends on a separate credit the bank does not control. If the sale side fails, through discrepancy, amendment or the buyer's bank refusing documents, the purchase credit still obliges the trader's bank to pay the supplier. Banks that do offer the structure police the mirror closely, which is one more reason the trader should find mismatches first.

How Phlo Systems helps

opsPhlo holds both legs of a back-to-back trade as one deal and runs a mirror check across the two credits: every point where the purchase credit is looser than the sale credit is flagged, with the field, the two conflicting values and the exposure explained, and the check re-runs as amendments land on either side. See the opsPhlo L/C workbench.

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Related reading:

• What is a letter of credit workability review, and when should it happen?
• MT700, MT707 and the current state of a letter of credit

Saurabh Goyal is the Founder & CEO of Phlo Systems. He has built finance and trading systems for commodity houses since 2008.