The market to book ratio divides the market value of a company’s equity by the book value of that same equity, so a result of 1.0 means the market is paying exactly the recorded amount and anything above it is paying for something the balance sheet does not carry. It is a market convention rather than a defined accounting measure: no US accounting standard sets it out, which is why the ratio’s numerator is unambiguous and its denominator is where practitioners disagree.
The same two figures inverted give the book to market ratio, and nothing else about the comparison changes.
The Two Routes, and Where They Part
Both of these are called the market to book ratio and they are not always the same number.
Route 1 market capitalization / book value of equity
Route 2 market price per share / book value per shareThey agree only when the two divisions use the same share population and the same slice of equity. A company with two classes of common stock trading at different prices has no single market price per share to put in Route 2, so Route 1 is the only honest one available. And where book value per share is computed on common equity alone while book value of equity in Route 1 still carries preferred stock, the two routes diverge by exactly the preferred balance.
Regulation S-X keeps those pieces visibly separate on the face of the balance sheet, which is what makes the discrepancy findable rather than mysterious. Preferred stocks that are not redeemable or are redeemable solely at the option of the issuer are stated under their own caption, common stocks under another, with the number of shares issued or outstanding and the dollar amount stated for each class of common on the face of the balance sheet (17 CFR 210.5-02, items 28 and 29).
The Preferred Stock That Is Not in the Denominator at All
There is a third position, and it changes the arithmetic before anyone gets to choose a route.
Preferred stock subject to mandatory redemption requirements, or whose redemption is outside the control of the issuer, is reported under its own caption ahead of the equity block rather than inside it (17 CFR 210.5-02, item 27), and which issues meet that test is worked through in redeemable equity. Only preferred that is not redeemable, or is redeemable solely at the issuer’s option, sits with the equity captions (17 CFR 210.5-02, item 28).
So a filer with mandatorily redeemable preferred already reports a book equity figure that excludes it, and subtracting preferred again to reach common book value would double count the adjustment.
What Sits Inside the Book Number
The rest of the equity block is a short list. Separate captions are shown for additional paid-in capital, other additional capital, retained earnings split between appropriated and unappropriated, and accumulated other comprehensive income (17 CFR 210.5-02, item 30).
Two of those deserve a second look before the ratio is computed. Accumulated other comprehensive income can be a large negative number on a company with pension or currency exposure, and it is inside book equity, so a ratio that looks high may be reporting a depressed denominator rather than an enthusiastic market. Retained earnings carry every historical loss the company ever took, so a long-established business that once wrote off an acquisition can show a thin book value with nothing currently wrong with it.
The Two Numbers Are Measured on Different Days
The numerator moves every second the market is open and the denominator is fixed at the last balance sheet date. A ratio quoted today against a book value from a quarter-end four months ago is comparing a live price with a stale measurement, and everything that happened in between (a buyback, a dividend, a quarter’s earnings) sits in one side and not the other.
That is not a flaw to correct so much as a caveat to state. What it rules out is treating a small movement in the ratio as information: for the ratio to move meaningfully, either the price has to move a lot or a new balance sheet has to arrive.
What the Ratio Cannot Tell You
The gap between the two figures is mostly structural rather than informational. A company cannot capitalize the brand, the client list or the reputation it built itself, and development spending is expensed as incurred, so a business whose value lives in people and software will always show a thin book value against its market value. That mechanism, and the cases where book runs above market instead, are worked through in book value of equity.
The ratio also breaks entirely at the boundary. Sustained losses or large buybacks can drive book equity to zero or below, and a negative denominator produces a number that is not a ratio at all, only a sign error waiting to be read as a bargain.
Common Questions
There is no threshold that travels across industries, because the size of the gap is set by how much of a business’s value the accounting rules never let onto the balance sheet. A software company and a utility can carry the same economics and report ratios several times apart. The defensible use is comparison within an industry and against the same company’s own history, and even then the ratio raises a question rather than answering it.
Take the market value of the equity, which is the share price multiplied by the shares outstanding, and divide it by the equity total on the most recent balance sheet. Decide once whether you are working with total equity or common equity only, then hold that choice on both sides of the comparison and across every company you compare. The share count itself is a reported figure rather than an estimate, stated for each class of common stock on the face of the balance sheet (17 CFR 210.5-02, item 29), and what moves it during a year is set out in outstanding shares.
Accountably places trained offshore accountants and tax preparers inside US CPA and EA firms, and a firm can put a block of its own equity roll-forward and reporting work through a trial task before a client engagement depends on it.
