The visibility gap
Supply chain cost management has a structural blind spot: market conditions and accounting reality are separated by weeks. When fuel prices spike or ocean capacity tightens, the effect on your freight invoices does not arrive immediately. It arrives weeks or months later, depending on how your freight is contracted.
This gap creates two compounding problems. First, finance teams are always reacting to the market of 30 to 90 days ago, not today's market. Second, procurement teams who watch spot market indices may believe costs are stabilizing while AP is about to receive a wave of invoices priced at the peak. These two teams can be looking at the same market and reaching opposite conclusions about their cost exposure - both correctly, because they are looking at different points in time.
Understanding the invoice lag is not a technical curiosity. It is the foundation of effective freight cost forecasting.
How freight invoices work
A freight invoice is not generated at the moment a carrier quotes a rate. It is generated after the cargo moves, consolidated across multiple surcharge line items, and posted to AP when the carrier's billing cycle closes. Each of these steps adds time between the market event and the accounting entry.
The key surcharge components that change with market conditions are:
- Bunker Adjustment Factor (BAF) / Fuel Surcharge (FSC): Updated monthly or quarterly by most carriers, referencing a published fuel index from the prior period. A fuel price spike in week 1 typically reaches your BAF line in the invoice covering weeks 4 to 8.
- Currency Adjustment Factor (CAF): Updated on a similar cycle, referencing FX rates from the prior calculation window.
- General Rate Increases (GRI) and Emergency Surcharges: These tend to apply faster - sometimes with as little as 2 weeks notice on spot bookings - but take longer to flow through contracted rates.
- War Risk / Piracy / Congestion Surcharges: These can apply within days on spot freight but may be absorbed for a contract period on fixed-surcharge contracts.
The result is a layered stack of surcharge mechanisms, each on its own billing and update cycle, each referencing market data from a different point in the past.
Three lag buckets
The Sirius model organizes this complexity into three lag buckets - M1, M2, and M3 - representing the three dominant contract structures in global freight. Each bucket has a characteristic realization lag: the typical time between a market event and when that event is reflected in an invoice.
| M1 - Spot | M2 - Short-term | M3 - Annual |
|---|---|---|
| ~30 day lag | ~60 day lag | ~90 day lag |
| Spot bookings, index-linked contracts, short-cycle tender agreements | 6-12 month contracts with quarterly surcharge reset mechanisms | Annual contracts with semi-annual or annual surcharge review clauses |
| Highest sensitivity to market moves. Cost pressure transmits fastest here. | Moderate buffering. Market shocks are absorbed for one quarter before resetting. | Strongest lag. Carrier absorbs cost pressure until the next review window. |
M1 - spot and index-linked
M1 represents freight purchased at or near spot market prices: open bookings, index-linked contracts that reprice monthly or faster, and short-cycle tender agreements where rates are reviewed at 30-day intervals. The typical invoice lag for M1 freight is approximately 30 days.
For a shipper with significant M1 exposure, a market event that occurs today will appear in invoices received roughly four to five weeks from now. The driver is not shipping time - it is billing cycle. Carriers accumulate charges across a freight period, issue an invoice at the end of the period, and the invoice enters AP workflow before it is posted and visible to finance.
M1 freight is the most responsive to market moves, which means it is also the highest-volatility contract tier. During a price spike, M1 costs can increase significantly within a single billing period. During a market correction, M1 is also the first to benefit.
M2 - short-term contracts
M2 represents freight under short-term contracts, typically 6 to 12 months in duration, where surcharge mechanisms are reviewed quarterly or semi-annually. The contractual structure provides a buffer: the carrier absorbs short-duration market moves within a quarter and passes them through at the next surcharge reset. The typical invoice lag for M2 freight is approximately 60 days.
The 60-day figure reflects both the billing cycle delay (similar to M1) and the surcharge update cycle. A fuel price spike that occurs early in a quarter may not appear in the surcharge adjustment until the start of the next quarter, adding 30 to 60 days beyond the billing cycle lag.
M2 contracts offer shippers more predictability than spot freight, but they create a false sense of insulation. A company that has locked in M2 surcharge rates through the end of a quarter may see their spot-watching procurement team declare that freight costs are rising while their current invoices show no increase - yet. The reset is coming.
M3 - annual contracts
M3 represents freight under long-term annual contracts where the surcharge mechanism is reviewed once or twice per year. The typical invoice lag for M3 freight is approximately 90 days, though in some structures the effective lag can extend to 120 to 150 days for shippers with mid-year contract anniversaries and semi-annual review clauses.
Annual contracts are the most insulating structure from a short-term volatility perspective - but they create the largest delayed exposure. A carrier absorbing a sustained cost increase across an entire contract period will reset aggressively at the next renewal. For shippers on annual contracts, the invoice surprise does not arrive as a small monthly increment but as a significant step change at renewal.
Annual contracts also create the longest gap between market intelligence and actionable response. By the time an M3 shipper sees the cost pressure in their invoices, the market event that caused it may have occurred three months ago. The window for contract renegotiation or modal rebalancing has typically already closed.
Why CFOs see cost surprises
The invoice lag is the primary reason finance teams are surprised by freight cost variances. The organizational structure of most companies amplifies the problem. Procurement watches market indices and adjusts expectations based on current spot conditions. Finance books invoices as they arrive and compares them to the prior period. These two streams of information are telling different stories about the same underlying market - one current, one lagged - and there is typically no function bridging the gap.
The consequence is that budget variance meetings consistently feature freight as an unexplained line. "We saw this in the market three months ago, why wasn't it in the forecast?" The answer is usually that the forecast was built on current market data without modeling the realization lag of the actual contract portfolio.
A less obvious consequence is over-correction. When finance sees a large freight cost spike in Q2 invoices, they may assume the market is still at that level and budget conservatively for Q3 - even though the market has since corrected. The lag cuts both ways: it delays the pain but also delays the relief.
How Sirius models the lag
The Sirius model addresses the invoice lag at the lane and modality level. Rather than reporting only the current week's spot pressure, Sirius calculates three parallel readings for each trade lane: the current market signal (M1 realization), the 60-day forward-realized reading (M2 projection), and the 90-day forward-realized reading (M3 projection).
This means a Sirius user looking at the Far East to Europe lane today sees not just what the market is doing now, but what is already locked into their M2 invoices and what is building toward their M3 renewal window. The three readings give finance and procurement a shared temporal reference - they are looking at the same market through three different time horizons.
For each trade lane, the M1/M2/M3 split is further weighted by modality, because the contract structure distribution is not uniform across ocean, air, and road. Ocean freight on major lanes tends to have more M2/M3 weight. Air freight tends toward M1. Road freight varies by region and carrier relationship.
The result is a forward-looking cost pressure signal that maps directly to how costs will appear in AP, rather than how the market looks today. For a finance team building a 90-day rolling freight cost forecast, this is the input that closes the gap between procurement intelligence and accounting reality.