What it means
Backlog is a stock, not a flow. It rises as new bookings arrive and falls as work is delivered and billed, so it behaves like a reservoir sitting between the sales team and the revenue line.
It matters because reported revenue looks backwards and backlog does not. A quarter of flat revenue with a sharply rising backlog describes a very different business from flat revenue with a shrinking one.
The awkward part is that a big backlog is not automatically good news. It can signal strong demand, or it can mean the delivery team cannot keep up, customers are waiting too long, and cancellations are already being drafted.
Analysts often convert it into time, asking how many months the business could keep producing at current rates without winning a single new order. They also watch the split between the portion expected to convert within twelve months and the part stretching further into the future.
Definitions vary, so it is always worth asking what has been counted. Some companies include only signed, non-cancellable contracts, while others fold in renewal options and verbal commitments, which makes the headline number far softer than it appears.
Quality matters at least as much as size. A backlog concentrated in one customer, priced before a cost increase, or full of contracts the buyer can walk away from at short notice is worth far less than the same total spread across many firm, currently priced orders.
In practice
Real-world examples
Example 1
A commercial roofing contractor carries a nine month backlog going into winter, which lets it keep crews on the payroll through the quiet season rather than laying them off and rehiring in spring.
Example 2
A software firm reports flat quarterly revenue but a backlog up 40% year on year, because it has shifted from annual to three year contracts. Revenue recognition is spread over a longer period, so the growth appears in backlog long before it appears in the income statement.
Example 3
A furniture maker's backlog reaches eighteen months after a supply problem, and cancellations start climbing as customers who were quoted six weeks discover they must wait until the following year. The sales director stops quoting the backlog as evidence of demand once the deposit refund line starts growing faster than new orders.
Think of it
A backlog is like a restaurant queue where customers have already paid for their meals. The kitchen knows exactly what needs to be cooked next, and the line shows how busy the chefs will be for the next hour.
Formula
Calculation
Closing backlog = opening backlog + new bookings - revenue recognised - cancellations
Months of cover = backlog / average monthly revenue
An engineering firm starts the quarter with a backlog of $20,000,000. During the quarter it books $6,000,000 of new orders, recognises $4,500,000 of revenue as work is delivered, and loses $500,000 to a cancelled contract. Closing backlog is $20,000,000 + $6,000,000 - $4,500,000 - $500,000 = $21,000,000.
Quarterly revenue of $4,500,000 means average monthly revenue of $4,500,000 / 3 = $1,500,000, so the backlog represents $21,000,000 / $1,500,000 = 14 months of cover. The book-to-bill ratio for the quarter is $6,000,000 / $4,500,000 = about 1.33, meaning the company won roughly a third more work than it delivered and the reservoir is filling rather than draining.Case study
Seen in the real world
This is an illustrative and entirely fictional case. Wrenfield Automation, an invented builder of packaging machinery, ended a strong year with a backlog of $34,000,000 against annual revenue of $24,000,000, and the board celebrated seventeen months of cover.
The finance director broke the number down and found it less comforting. Two customers accounted for $19,000,000 of it, one contract worth $7,000,000 allowed cancellation on thirty days' notice with no penalty, and $6,000,000 had been priced eighteen months earlier before steel costs rose by a quarter, so it would be delivered at a loss.
In this fictional example the response was to report backlog in three bands from then on: firm and profitable, firm but margin at risk, and cancellable. The headline stayed at $34,000,000, but the board finally understood that only about $21,000,000 of it was work they could count on at the margins originally assumed.
Watch out
Common mistakes
- Reading a growing backlog as pure good news, without checking whether it reflects strong demand or a delivery bottleneck.
- Treating backlog as revenue, when it becomes revenue only as the work is actually performed and can still be cancelled or repriced.
- Quoting a single total without disclosing customer concentration, cancellation rights or how much sits beyond twelve months.
Questions
People also ask
Is backlog the same as deferred revenue?
No, because deferred revenue is cash already received for undelivered work and sits on the balance sheet, whereas backlog is mostly uninvoiced and appears only in commentary.
What is a healthy level of backlog?
Enough to cover the planning and hiring cycle, commonly three to twelve months depending on the industry, without stretching so far that customers start leaving.
How does backlog relate to bookings?
Bookings are the new orders won in a period and backlog is the running total of orders still waiting to be delivered.