Least-Cost Routing: Sending Payments to the Cheapest Eligible Rail

Least-cost routing means different things depending on which market you are operating in. In Australia, it is a formally defined, regulator-mandated capability tied specifically to dual-network debit cards. Globally, the underlying logic — directing each transaction to the cheapest eligible rail — is increasingly how sophisticated operators think about their payments stack.

This article covers both: the Australian LCR framework as the anchor case, and the broader cost-based routing decision logic that applies wherever multiple rails are available.

The Australian LCR Framework

Dual-network debit and the RBA mandate

Australian debit cards are co-badged. Most carry both the eftpos domestic scheme and a Visa or Mastercard debit brand. When a cardholder taps or inserts a co-badged card, the terminal has a choice: process through eftpos, or process through the international scheme.

Before least-cost routing, terminal defaults typically sent transactions through the international scheme — a product of how payment terminals were configured by acquirers who had commercial relationships with the international networks. This systematically directed volume away from eftpos even when eftpos was the lower-cost option for the merchant.

The Reserve Bank of Australia has been clear on the purpose of LCR: to promote competition in the debit market and reduce payment costs for merchants. LCR gives merchants the ability to set their own routing preference, directing dual-network debit transactions through the network that costs them less.

How the cost difference arises

Interchange and scheme fees for eftpos domestic debit transactions are typically lower than the equivalent Visa or Mastercard debit transaction in Australia. The spread is most pronounced for everyday, low-average-ticket categories: grocery, fuel, pharmacy, quick-service restaurants. For these merchants, card-present debit transactions dominate the volume, and a consistent routing preference to eftpos where cheaper produces meaningful cost savings across the aggregate.

The differential is smaller for card-not-present transactions (e-commerce), which is why CNP LCR was implemented later and required additional work from PSPs.

PSP implementations

Stripe automatically implements LCR for eligible Australian merchants using dual-network debit cards. No additional configuration is required — Stripe routes to the lower-cost network automatically for qualifying transactions.

Adyen supports card-not-present LCR for eftpos in Australia, allowing merchants to capture the cost benefit on e-commerce transactions as well as card-present.

Most major PSPs operating in Australia now support LCR in some form. Merchants with legacy configurations should confirm with their PSP whether LCR is active and whether CNP transactions are included.

The Cost Calculation Methodology

Whether you are configuring LCR in Australia or building cost-based routing logic globally, the decision framework is the same.

Step 1: Identify available rails for this card/transaction type

For a given card BIN and transaction, what rails are available? A co-badged debit card in Australia has two. A Visa credit card has one. A bank account in India transacting via UPI has a different rail entirely.

Step 2: Calculate the effective cost per rail

Effective cost = interchange + scheme fees + acquirer margin. For MDR comparison: all three components must be included. A rail with lower scheme fees but higher acquirer margin may not be cheaper in practice. Pull the actual settlement data and calculate effective bps per rail from real transaction history, not just the rate card.

Step 3: Adjust for authorization rate differences

This is where naive cost routing goes wrong. If Rail A costs 1.5% and Rail B costs 1.7%, Rail A appears cheaper. But if Rail B has a 2% higher authorization rate, the effective revenue per transaction attempt is higher on Rail B for any transaction with positive margin. The correct formula:

Expected net revenue per attempt = (transaction value × margin) × authorization rate − (MDR × transaction value)

Run this for both rails. The cheaper-in-MDR option is not always the better economic choice.

Step 4: Configure routing preference in your PSP or gateway

Once the economics are clear, configure the preference. Most modern PSPs expose routing configuration — either automatically (Stripe LCR) or through explicit settings. For multi-PSP environments, orchestration layers like Spreedly, Primer, or Gr4vy enable this logic at the orchestration layer rather than per-PSP.

Cost-Based Routing Beyond Australian LCR

LCR as a formal construct is specific to Australia. In other markets, operators build equivalent routing logic without the regulatory mandate, typically across three categories:

Domestic scheme routing

Many markets have domestic card schemes with lower interchange economics than international Visa/Mastercard:

• India: RuPay (NPCI) carries zero MDR on debit transactions by government mandate. A merchant processing Indian debit cards routes to RuPay domestically and saves the entire card acceptance cost on that transaction.
• France: Cartes Bancaires is co-badged on over 95% of French cards. CB domestic interchange is typically lower than international scheme interchange for domestic transactions.
• Belgium: Bancontact dominates domestic debit with similar economics to eftpos in Australia.
• Brazil: Elo and domestic debit rails have different economics from international Visa/Mastercard on Brazilian-issued cards.

The interchange-plus pricing model is essential for this optimization — if you are on blended pricing, the PSP captures any domestic/international interchange differential. On IC+ pricing, that saving flows through to you.

A2A rail routing

Real-time payment rails in many markets carry near-zero or zero MDR:

• UPI (India): zero MDR mandate for merchant transactions
• PIX (Brazil): near-zero for merchants under most implementation structures
• PayNow (Singapore): zero MDR for most merchant implementations
• SEPA Instant (EU): typically lower cost than card MDR for A2A credit transfers

The economic case for offering A2A checkout alongside card is straightforward: every transaction that migrates from card to A2A reduces payment cost substantially. The friction cost is the UX change — adding a payment method option, handling the redirect or in-app A2A flow.

The decision rule: if (card MDR − A2A MDR) × volume migrated > cost of A2A integration + conversion rate decline, add the rail. For merchants with high AOV and digitally sophisticated customers in markets with strong A2A adoption, this calculation often favors adding the rail.

Multi-acquirer routing for cost optimization

The broader multi-acquirer routing framework includes cost as one dimension alongside authorization rate, resilience, and geographic coverage. When you have two acquirers for the same market, routing logic can direct certain card types or BIN ranges to the acquirer with better economics for that transaction profile.

This is the advanced version of cost routing — not just selecting the cheapest rail by type, but using ML-based routing to optimize the acquiring path for each individual transaction against a cost + authorization rate objective function.

When Cost Routing Creates Tension

Scheme rules

Card schemes have rules about network routing that operators must comply with. Visa and Mastercard rules govern how transactions on their branded cards are processed. Systematically routing away from an international scheme brand entirely may conflict with acceptance requirements depending on your acquirer agreements and scheme licensing terms. Review your specific contracts before configuring aggressive routing preferences.

UX trade-offs

A payment UI that presents four payment options is not automatically better than one that presents two well-chosen ones. Offering A2A as an alternative creates choice — and choice creates potential abandonment for customers who prefer card. The cost saving per transaction needs to be weighed against any conversion rate impact at checkout.

For high-intent, high-AOV contexts (B2B invoices, large software purchases, subscription renewals), A2A checkout typically has minimal conversion impact. For low-intent, impulse contexts, adding friction to the payment flow may cost more in conversion than it saves in MDR.

The auth rate point economics framework applies here: before optimizing for cost, understand the revenue value of your current authorization and conversion rates — cost optimization that reduces either should be evaluated net of that revenue impact.