There is a quiet line in every institutional FX broker's P&L that no marketing deck mentions: the funding cost of the inventory they are carrying for you. It is paid in basis points per day, it varies with the broker's own balance-sheet position, and on the days the broker's funding curve moves, your spread moves — for reasons that have nothing to do with your trade and everything to do with the broker's overnight repo desk.
Understanding the structure of that cost is the difference between a counterparty relationship that is durable through a stress cycle and one that quietly degrades the first time conditions tighten.
Where the cost comes from
When you take liquidity from a broker, the broker either internalises the position into its existing inventory or externalises it via a hedge to a wholesale counterparty. The internalised portion sits on the broker's balance sheet and costs the broker funding — overnight, term, and through any unscheduled events that require additional margin against that position.
The funding cost is real and is paid in two ways: an explicit interest cost (the broker is borrowing to fund the position, either via repo against collateral or via unsecured funding lines) and an implicit capital cost (the position consumes regulatory capital, which has an opportunity cost relative to its alternative deployment).
On a calm Tuesday with abundant funding liquidity and stable rates, the cost is a small known number. On a Wednesday after a hawkish central-bank surprise, the cost rises across the entire industry simultaneously, and brokers' streaming spreads widen in lockstep. Most desks experience this as 'spreads widened today' without ever connecting it to the underlying funding-curve shift.
The three components of funding cost
Overnight
The base case. The broker funds the position overnight in repo against the position itself or in unsecured funding from its treasury. The cost is the overnight rate plus the broker's spread to that rate. For a tier-1 institutional broker the unsecured spread is typically 5-20 bps; for a leveraged-broker model financed via term repo it can be 50-150 bps. Both numbers are floors, not ceilings.
Term
Positions held beyond overnight need term funding, which the broker procures in 1-week to 3-month repo or via the unsecured CP/CD market. The term curve is upward-sloping in normal conditions and inverts in funding stress; an inverted curve is one of the strongest leading indicators that broker spreads are about to widen materially.
Stress
On days when the funding market itself is dislocated — repo specials, CCP margin calls, dealer-balance-sheet constraints around quarter-end — the funding cost spikes by an order of magnitude beyond its normal level. The broker that has not pre-positioned for this experience tightens its spread in real time; the broker that has pre-positioned widens by less.
How this manifests as spread
Brokers that are funding-sensitive widen their spreads on the entire book during a funding-stress day, even on instruments where the underlying market is calm. This is the mechanical answer to the question 'why did my major-pair spread widen today even though nothing happened in the major-pair market'.
Brokers that are funding-resilient — well-capitalised, multi-source funded, with longer-dated funding to match their position lifetimes — widen by less and on a narrower subset of instruments. The differential is observable. A desk that tracks its own historical spread paid to each broker against a public funding-stress index (the FRA-OIS basis, the IOR-RRP differential, dealer CDS spreads) can quantify each broker's funding sensitivity within a quarter of trading data.
What to ask your counterparty
- What is the average overnight funding cost embedded in your streaming spread on major pairs? A counterparty that cannot answer this is either uninformed about its own cost or unwilling to disclose it; both are signals.
- What proportion of your funding is overnight versus term? An overnight-dominated funding stack widens more during funding stress; a term-dominated stack is more stable but charges a higher base.
- Do you pre-position term funding against expected residual inventory, or do you fund it overnight by default? The answer to this question maps directly to the spread behaviour you will see during quarter-end and year-end.
- What is your unsecured funding spread to the relevant overnight reference rate? Tier-1 institutional brokers are at 5-20 bps; anything materially wider is information about counterparty risk.
Drovix's funding profile
Drovix funds its institutional book through a mix of overnight secured repo against position collateral and term unsecured lines from a panel of tier-1 banks. The mix is approximately 30/70 overnight/term, deliberately weighted toward term to reduce the funding-stress sensitivity of the streaming book. The unsecured spread is publishable on request; the term tenor distribution is publishable on request.
The architecture that allows us to internalise efficiently — and therefore reduce the funding cost of any given inventory level — is part of what makes the spreads we publish economically sustainable. See The Architecture of a Fair Spread for the pricing side; this post is the cost side.
None of this is unique to Drovix in principle. What is increasingly unique in practice is the willingness to discuss the funding stack explicitly with a counterparty who asks. A broker that treats its funding model as confidential is a broker who has not stress-tested its own assumptions and is going to find out alongside its counterparties whether they hold.
Where to go next
→ Institutional Onboarding and Counterparty Due Diligence — the rest of the questions worth asking a counterparty before you start sending size.
→ Correlation Under Stress — the related question of how funding stress and market stress propagate together, and what that means for a hedge's reliability.
Methodology and data
Balance-sheet cost is computed as the all-in funding rate (PB margin + haircut + repo + capital charge) applied to a constant-notional position, expressed in pips per day for FX and in basis points per day for index-CFD. The sample is nine tier-1 PBs and four non-bank prime brokers across the trailing eighteen months. Costs are normalised to a standard reference book; cross-margin offsets and netting benefits are excluded for comparability.
Limitations and scope
PB pricing schedules are commercially negotiated; the published figures here are central-tendency estimates, not quotes. Cross-margin offsets and netting can reduce balance-sheet cost by 20–40% for diversified books, and this benefit is not reflected in the comparable figures. Non-bank PB costs are stable in normal conditions but rerate faster in stress than tier-1 PB costs do.
Further reading
→ Margin Procyclicality and Tier-1 Stress — The stress side of the same cost function. See /blog/margin-procyclicality-tier1-stress.
→ Capacity Planning for Execution Strategies — How the balance-sheet cost flows into per-strategy capacity. See /blog/capacity-planning-for-execution-strategies.
Drovix Research is the in-house institutional desk of Drovix MU Ltd, regulated by the Financial Services Commission of Mauritius. All notes are informational only and do not constitute investment advice, a solicitation, or a recommendation to transact in any financial instrument.
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Institutional Research
Drovix Research Desk publishes institutional-grade analysis covering macro events, cross-asset correlations, and execution insights for professional market participants.