Why one year tells you nothing
You have spent the whole ladder learning to build the statements; now you cross over to *reading* them. And the first hard truth of reading is that a lone figure is almost mute. Suppose a company reports net income of 80,000. Is that good? You genuinely cannot say. Good compared to last year's 120,000? Then it is a collapse. Good compared to a rival earning 80,000 on one-tenth the sales? Then it is dismal. A number means something only against a yardstick — an earlier period, a base total, a competitor, or an industry norm. Analysis is, at heart, the discipline of never reading a figure alone.
This rung gives you the yardsticks. The two most basic ones use nothing but the statements themselves and a little arithmetic — no special data, no fancy software. [[horizontal-analysis|Horizontal analysis]] reads *across* the page: it places this year beside last year and measures how each line *changed*. [[vertical-analysis|Vertical analysis]] reads *down* the page: it expresses every line as a percentage of one base total, exposing the *structure* of the business. Change and structure — direction and shape. Master these two before you ever reach for a single ratio, because they are where the questions worth asking first appear.
Horizontal analysis: reading change across years
Horizontal analysis answers one question for every line: *how much did this change, and how fast?* You compute two things. First the absolute change — simply this year minus last year, in dollars. Then the percentage change — that dollar change divided by the *earlier* (or *base*) year, turned into a percent. The base year always goes in the denominator; getting that backwards quietly inverts your whole reading. This is why real reports print [[comparative-figures|comparative figures]] — last year's column set right beside this year's — precisely so the change is easy to read line by line.
Last year This year $ change % change
Net sales 200,000 250,000 +50,000 +25.0%
Cost of goods sold 120,000 160,000 +40,000 +33.3%
Gross profit 80,000 90,000 +10,000 +12.5%
% change = $ change / base (last) year
e.g. sales: 50,000 / 200,000 = +25.0%
COGS: 40,000 / 120,000 = +33.3%Read that little table the way an analyst would. Sales up 25% looks like a triumph — until your eye slides one row down and sees that [[cost-of-goods-sold-line|cost of goods sold]] climbed even faster, at 33%. The gap is the whole story: costs are outrunning sales, so [[gross-profit|gross profit]] rose a feeble 12.5%, and if the trend holds, a year of 'record sales' could end in *lower* profit. None of that is visible in either year's statement alone. It appears only when you read across, line by line, comparing each item to its own past.
Vertical analysis: reading structure down a column
Now turn ninety degrees. Vertical analysis ignores other years entirely and instead asks, *within this one statement, how is the whole carved up?* It expresses every line as a percentage of one chosen base on the same statement. On the [[income-statement|income statement]], the base is net sales, set to 100%; every line below is its slice of sales. On the balance sheet, the base is total assets, set to 100%; every asset, liability, and equity item is its slice of the total. Reading down the column, you see the *anatomy* of the business — where each dollar of sales goes, or how the company's resources are funded.
Take the same firm's income statement and recast it vertically. Of every 100 dollars of sales, suppose cost of goods sold eats 64, leaving gross profit of 36; operating expenses take 22; interest and tax take another 6; so net income is 8% of sales. Stated that way, the cost structure leaps off the page: you can *see* that almost two-thirds of every sales dollar is swallowed by the cost of the product itself before a single other bill is paid. That instant, structural read is exactly what raw dollars cannot give you, no matter how long you stare at them.
The real magic of vertical analysis is that it *strips away size*. A corner cafe and a national chain cannot be compared in raw dollars — one earns thousands, the other billions. But express both 'per 100 of sales' and they stand on perfectly equal footing: if the cafe spends 20% of sales on rent and the chain spends 6%, you have learned something true about each, regardless of scale. This is also how you compare a company against industry averages, which are themselves published as percentages. Note one subtle point: vertical analysis is *static* — it photographs a single period's shape, saying nothing about whether that shape is improving or decaying. For that, you still need the horizontal view.
Common-size statements: both views at once
When you apply vertical analysis to an *entire* statement at once — recasting every single line as a percentage of the base — you have built a [[common-size-statements|common-size statement]]. It is just vertical analysis written out in full, but giving it a name matters, because the common-size form is the workhorse of real comparison. On a common-size income statement net sales is 100% and every line is its percentage of sales; on a common-size balance sheet total assets is 100% and every line is its percentage of total assets. A firm with 5 million in sales and one with 5 billion can now sit side by side, their cost structures directly comparable even though the dollars differ a thousandfold.
Here is where the two tools fuse into something more powerful than either alone. Put several years of common-size income statements *side by side*, and you are now reading vertically (each year's structure) and horizontally (how that structure shifts over time) in a single glance. Imagine cost of goods sold reading 60%, 62%, 64%, 66% over four years while gross profit slides 40%, 38%, 36%, 34%. The dollars of sales might be climbing the whole time — but the *shape* is quietly deteriorating, the product getting less profitable year after year. That creeping erosion is invisible in raw figures and invisible in any single year; only the common-size trend reveals it.
Be honest, though, about what common-size hides: it shows proportions only, never amounts or absolute health. A business can have a perfectly normal-looking cost structure — every percentage right in line with peers — and still be far too small to survive, or be shrinking while its percentages hold flat. Worse, because everything is a percentage of one base, a swing in the *base itself* shifts every other line's percentage even when those lines, in dollars, never moved. A common-size statement is a lens for shape, not a scoreboard for size; always keep the absolute totals in view beside it.
Trend analysis: the long view over five years and more
Horizontal analysis usually compares two years. Stretch the same idea across five, ten, or more periods and it earns its own name: [[trend-analysis|trend analysis]]. The standard technique picks one year as the base, sets each of its figures to an *index* of 100, and restates every later year relative to it. If sales were 200,000 in the base year (= 100) and 240,000 three years on, the index is 240,000 / 200,000 = 120 — sales are 20% above base. Do this for several lines across many years and patterns surface that any two-year comparison would miss entirely.
Picture five years of two indexed lines, base year set to 100. Net sales reads 100, 108, 119, 131, 142 — a steady, satisfying climb of 42%. But net income reads 100, 101, 99, 96, 93 — it has quietly *fallen* to 93% of where it began. The five-year picture tells a story a single year could never tell. Something is steadily eating the gains: costs creeping up, prices being cut to win volume, interest mounting on new debt. You do not yet know *which*, but trend analysis has done its essential job — it has handed you the precise, urgent question to investigate. That is what good analysis is: not a verdict, but a sharp question pointed at exactly the right place.
Trends carry real dangers, so hold them loosely. A trend assumes the past predicts the future, which it frequently does not. Inflation can make a 'rising' sales trend pure illusion — selling the same quantity at higher prices looks like growth but is not. And a change in accounting method, or a single acquisition mid-period, can bend the line for reasons that have nothing to do with the underlying business. Whenever you choose a base year, make sure it was *typical*: pick a freak year as your '100' and every comparison to it inherits the distortion.
Putting it together — and where this leads
These tools are not rivals; they are partners, each answering what the others cannot. A disciplined first pass at any set of statements runs through them in order, and you can do it on the back of an envelope.
- Go vertical first. Recast this year's statement as common-size to see its shape — where each dollar of sales goes, how assets are funded. Ask: does this structure look reasonable for the industry?
- Then go horizontal. Compare this year to last in both dollars and percent, watching for lines that grew faster or slower than sales. Ask: what changed, and is any line moving the wrong way?
- Then stretch the trend. Line up five or more years, indexed to a typical base, and look for lines pulling apart — sales and profit diverging, debt outpacing equity. Ask: where is this business actually heading?
By now you should feel the shared spirit of all three: each one takes a flat page of numbers and gives it a *reference point* — a prior year, a base total, a long base period — so that figures which were mute begin to speak. They cost almost nothing to compute and they sharpen the right questions before you spend effort on anything fancier. But notice their shared ceiling: they describe *what* and *how much*, never quite *how well*. Is a 36% gross margin good? Is a current asset structure safe? For judgments like that you need to divide one figure by another — which is precisely what [[ratio-analysis|ratio analysis]], the work of the rest of this rung, is built to do. Horizontal and vertical analysis are the doorway; the ratios are the rooms beyond it.