Bill to book usually refers to the book-to-bill ratio, the value of new orders booked in a period divided by the amount billed in that same period. The answer is a ratio rather than a dollar amount: above 1.0 says more work came in than went out on invoices, below 1.0 says the reverse, and 1.0 says the two matched. The order of the two words moves around in ordinary use, the arithmetic does not, and bookings is always the numerator.
The Formula
Both inputs cover one window.
book-to-bill = bookings for a period / billings for the same periodBookings is the value of the new orders accepted in the period, which for a service business is the fee value of the engagements signed. Billings is the amount invoiced in that period. Both figures have to cover the same window.
Both Inputs Are Company-Defined
This is a company-defined operating metric rather than a figure lifted off a financial statement. Metrics of this kind can vary significantly from company to company and industry to industry, depending on various facts and circumstances (SEC, Commission Guidance on Management’s Discussion and Analysis of Financial Condition and Results of Operations, Release No. 33-10751), which is why two sources can quote the same ratio and mean different things by it.
Where a public company puts one in the management discussion and analysis section of a filing, the SEC would generally expect three things to accompany it, based on the facts and circumstances: a clear definition of the metric and how it is calculated, a statement of the reasons it provides useful information to investors, and a statement of how management uses it in managing or monitoring the performance of the business (SEC, Commission Guidance on Management’s Discussion and Analysis of Financial Condition and Results of Operations, Release No. 33-10751). That guidance took effect on February 25, 2020, and it also asks a company that changes how it calculates or presents a metric to consider disclosing the differences against the earlier presentation and whether the earlier figures should be recast.
None of that binds a private firm tracking the number for itself. It is still the right discipline, because a book-to-bill series is only readable against its own history, and a quiet change to what counts as a booking is indistinguishable from a change in demand.
Billings Are Not Revenue
The denominator counts invoices raised, and the date on an invoice does not decide the period the revenue belongs to, which arrears billing works through. Work already delivered and not yet invoiced is carried as accrued revenue and sits outside the period’s billings entirely.
So a ratio built on invoices raised and a ratio built on revenue recognized answer different questions, and both versions circulate under the same name. State which one produced the number.
How a CPA Firm Reads It
For a firm, bookings is the fee value of the work accepted in the period, the engagement letters signed and the scope extensions agreed, and billings is what actually went out on invoices. A reading above 1.0 held across several periods means work is being taken on faster than it is being delivered and billed. That shows up first as unbilled work in progress and then as a due date the firm cannot hold, so the first thing it flags in a firm is capacity, and the levers for it are the ones set out in accounting firm capacity planning.
Seasonality distorts a short window badly. A tax practice signs most of its season’s work early in the year and bills through the spring, so a single month’s ratio moves on the calendar rather than on demand. Read it on a rolling window that covers a full cycle, and against the same window a year earlier.
A Worked Example
Say a firm’s engagement and billing records for two quarters carry the figures below.
Quarter 1 Quarter 2 Combined
Bookings, fee value signed 300,000 210,000 510,000
Billings, fees invoiced 240,000 300,000 540,000
book-to-bill 1.25 0.70 0.94The first quarter took in more work than it billed and the second billed down what the first had booked, so the half year, rounded, reads just under one. Reading the two quarters together matters here, because the two inputs are not the same work: the numerator is demand arriving, and the denominator is delivery of demand that mostly arrived earlier.
What It Is Not
Backlog is the closest neighbor, and the difference is stock against flow. Backlog is a balance at a date, the work sold and not yet delivered, while book-to-bill is a ratio across a period. Backlog rises when bookings run ahead of the work actually delivered, so a period above 1.0 points the same way only to the extent billings track delivery.
It is also not a collection measure. Billing is the invoice and not the money, and how long an invoice then takes to turn into cash is what accounts receivable and the cash conversion cycle count.
Common Questions
Book-to-bill is the standard rendering of the same ratio: the period’s bookings divided by the period’s billings. A single reading says little on its own, so it is normally read as a series, where a run above 1.0 means orders are arriving faster than they are being invoiced and a run below 1.0 means the reverse.
Take the value of the orders booked in a period, divide by the amount billed in that same period, and state both definitions and the window alongside the answer. Nothing in the arithmetic fixes what counts as a booking, so that decision gets made once and then held.
A different thing entirely, and unrelated to the ratio. A bill book is the physical duplicate invoice pad a business writes bills out of, printed in carbonless sets so the seller keeps a copy of every bill issued.
It carries several senses and the context settles which one is meant. To book a transaction is to record it in the accounting records, the work bookkeeping covers, and the books are those records taken together. Book value is separate again, a carrying amount on the balance sheet rather than a market price.
Accountably places trained offshore accountants and tax preparers inside US CPA and EA firms, and a firm whose bookings are running ahead of delivery can put a real block of its own work through a trial task before anything client facing depends on it.
