Contents
Finance & Investing
Section 1
The Core Idea
Financial ratios compress a company's financial statements into comparable, interpretable numbers. They answer questions like: How profitable is this business? How leveraged? How efficiently does it use capital? Ratios let you compare companies of different sizes, across time, and against benchmarks. A single number — return on equity, debt-to-EBITDA, current ratio — can summarise a dimension of performance or risk.
The main categories are profitability (margins, ROE, ROIC), liquidity (current ratio, quick ratio), leverage (debt/equity, interest coverage), and efficiency (asset turnover, inventory days). Each ratio is a fraction: one line item divided by another. The numerator and denominator must be chosen so the ratio is meaningful. Revenue margin is profit over revenue; ROE is net income over equity. The same inputs can be combined in different ways for different questions. The discipline is to know what each ratio measures and what it doesn't — and to use several ratios together rather than one in isolation.
Ratios are not truth; they are summary statistics. They can be gamed (window-dressing balance sheets, shifting revenue recognition), and they reflect accounting choices (GAAP vs non-GAAP, depreciation, leases). They also lag: they describe the past. For forecasting and valuation, ratios are inputs — they help you understand the business and build assumptions — but the output (value) comes from cash flow and discounting. Use ratios to screen, compare, and diagnose; don't confuse a good ratio with a good investment.
Section 2
How to See It
Financial ratios reveal themselves whenever performance or risk is summarised in a single number derived from the financial statements. The diagnostic: is this a line item divided by another (or a combination of items)? If yes, it's a ratio.
Business
You're seeing Financial Ratios when a board reviews "margins," "ROE," or "cash conversion." Each is a ratio — gross margin = gross profit / revenue; ROE = net income / equity; cash conversion = operating cash flow / net income. The board uses them to track performance and compare to prior periods or targets.
Technology
You're seeing Financial Ratios when a SaaS company reports "net revenue retention," "CAC payback," or "rule of 40." NRR is a ratio (retained + expansion revenue / prior period revenue); CAC payback is CAC / (ARPU × margin); rule of 40 combines growth rate and profit margin. Each compresses operational and financial data into a metric.
Investing
You're seeing Financial Ratios when an investor screens for "P/E under 15," "debt/EBITDA below 3x," or "ROIC above 12%." P/E is price / earnings; debt/EBITDA is net debt / EBITDA; ROIC is NOPAT / invested capital. Ratios enable cross-sectional comparison — which companies are cheap, leveraged, or earning their cost of capital?
Markets
You're seeing Financial Ratios when credit analysts cite "interest coverage" or "current ratio" to assess default risk. Interest coverage = EBIT / interest expense; current ratio = current assets / current liabilities. The ratios summarise ability to service debt and meet short-term obligations. They are inputs to ratings and pricing.
Section 3
How to Use It
Decision filter
"When evaluating a company or a project, ask: which ratios capture what I care about — profitability, risk, efficiency? Compute them, compare to peers and history, and check for consistency. Use ratios to screen and diagnose; then dig into the drivers. Don't let a single ratio override the full picture."
As a founder
Manage to the ratios that matter for your stage and model. Early-stage: burn multiple, runway, gross margin. Growth: revenue growth, CAC payback, NRR. Mature: ROIC, free cash flow margin, leverage. Report the same ratios consistently so you and your board can track progress. Benchmark against comparable companies. When a ratio deteriorates, diagnose the numerator and denominator — is it revenue, cost, or balance sheet? Fix the driver, not the ratio in isolation.
As an investor
Use ratios to screen and compare. Profitability (margins, ROE, ROIC), leverage (debt/EBITDA, interest coverage), and valuation (P/E, EV/EBITDA) are the starting set. Compare to sector and history. When a company looks "cheap" on P/E but has falling ROE and rising debt, the ratio is a signal to dig deeper — not a buy. When ratios are strong and improving, understand why (sustainable vs one-time). Ratios are the first pass; cash flow and quality of earnings are the second.
As a decision-maker
When approving budgets, acquisitions, or partnerships, request the key ratios. For an acquisition: margins, ROIC, leverage, and how they compare to our own and to sector. For a division: same. Ratios give a common language. Track them over time so you see trends. When someone presents a single impressive ratio, ask for the full set — one ratio can hide weakness elsewhere.
Common misapplication: Optimising one ratio at the expense of others. Cutting R&D to boost short-term margins can hurt ROIC and growth. Taking on debt to buy back stock can improve ROE while increasing risk. Ratios are linked; improving one can worsen another. Optimise for the right combination, not a single number.
Second misapplication: Treating ratios as causal. A high ROE doesn't cause value — it may reflect leverage or accounting. A low P/E doesn't mean the stock is cheap — earnings may be cyclical or overstated. Ratios are descriptive. Use them to understand and compare; don't assume the ratio itself is the strategy.
Section 4
The Mechanism
Section 5
Founders & Leaders in Action
Warren BuffettChairman & CEO, Berkshire Hathaway
Buffett uses ratios as a first filter — ROE, debt levels, margins — but he always digs into the quality of earnings and the drivers. He has said he looks for businesses that earn high returns on equity without much leverage, and that have consistent margins. The ratios point him to businesses worth studying; the deeper analysis determines whether he invests. He also adjusts for accounting: he focuses on owner earnings and looks through one-time items so the ratios reflect sustainable performance.
Michael BloombergFounder & CEO, Bloomberg L.P.
Bloomberg built a terminal that made financial ratios and data ubiquitous. The company's value was in standardising and delivering ratios (and raw data) so that analysts could compare companies instantly. The lesson: ratios are useful only when they're consistent and comparable. Bloomberg's product is the infrastructure that makes ratio-based analysis possible at scale.
Section 6
Visual Explanation
Financial Ratios — Numerator / denominator. Profitability (margins, ROE), liquidity (current ratio), leverage (debt/EBITDA), efficiency (turnover). Compare across time and peers; use with cash flow and quality of earnings.
Section 7
Connected Models
Financial ratios summarise the output of the business and its financial structure. The models below either use ratios as inputs (DCF, valuation), complement them (cash flow, margin of safety), or explain their components (leverage, working capital).
Reinforces
Discounted Cash Flow
DCF values a company from projected cash flows and a discount rate. Ratios are inputs: you use margins, growth, and capital intensity (from ratios) to build the projections. Historical ratios inform what's sustainable; you don't value from ratios directly, but ratios inform the assumptions.
Reinforces
Margin of Safety
Margin of safety is buying below value. Value is often estimated using DCF or multiples; multiples are ratio-based (P/E, EV/EBITDA). A margin of safety might mean buying at a P/E below the sector average or below the company's history. Ratios help you see how much "margin" you're getting.
Tension
Cash Flow
Ratios are often based on accrual earnings; cash flow is actual cash. A company can have strong ratios (high ROE, margins) and weak cash flow (working capital build, capex). The tension: ratios can look good while the business consumes cash. Use both — ratios for profitability and structure, cash flow for liquidity and sustainability.
Tension
Profitability
Profitability ratios (margins, ROE) measure return; they don't measure risk or sustainability. A high-margin business with declining revenue or rising competition may not be a good investment. Ratios are a snapshot; profitability as a model asks whether the return is durable. The tension is between "looks profitable" and "will stay profitable."
Leads-to
Leverage
Leverage ratios (debt/equity, debt/EBITDA, interest coverage) summarise financial risk. High leverage amplifies returns when things go well and amplifies losses when they don't. The ratio is the first step to understanding how much risk the capital structure imposes.
Leads-to
Working Capital
Working capital ratios (current ratio, inventory days, receivables days) summarise liquidity and efficiency. They lead to questions about cash conversion and operational discipline. Improving working capital ratios can free cash without changing profitability.
Section 8
One Key Quote
— Benjamin Graham, Security Analysis"The purpose of ratio analysis is to simplify the comparison of companies and periods. But the analyst must never forget that the ratio is a summary — it can hide as much as it reveals. Always look at the components."
Ratios are a starting point. The numerator and denominator each have a story — why did margin expand? Was it revenue mix, cost cut, or one-time? The practitioner's job is to use the ratio to focus, then to open the hood and understand the drivers.
Section 9
Analyst's Take
Faster Than Normal — Editorial View
Use a set of ratios, not one. No single ratio tells the full story. Profitability, leverage, liquidity, and efficiency together give a picture. A company can have great margins and unsustainable debt; great ROE and negative cash flow. The set protects you from the seductive single metric.
Compare and trend. A ratio in isolation is hard to interpret. Compare to sector, to history, and to the cost of capital (for return ratios). Is ROE above 12%? Is it improving or declining? Trend often matters more than level — deterioration in key ratios is an early warning.
Adjust for accounting and one-times. GAAP ratios can be distorted by stock-based comp, restructuring, or acquisition accounting. Normalise where possible so ratios reflect sustainable performance. Non-GAAP abuse is real; use judgment.
Ratios screen; cash flow and quality decide. Use ratios to find candidates and to rule out obvious problems. Then go to cash flow — does the business generate cash? — and quality of earnings — is the profit real and repeatable? Ratios get you to the shortlist; deeper analysis gets you to the decision.
Section 10
Test Yourself
Is this mental model at work here?
Scenario 1
A company reports gross margin of 60% and net margin of 5%. An analyst says 'high gross margin is being eaten by opex.'
Scenario 2
A CEO focuses only on improving ROE. She takes on more debt and buys back stock. ROE rises; the stock price falls over the next two years.
Section 11
Summary & Further Reading
Summary: Financial ratios compress the financial statements into comparable metrics — profitability (margins, ROE), liquidity (current ratio), leverage (debt/EBITDA), efficiency (turnover). They enable comparison across companies and time. Use a set of ratios to screen and diagnose; compare to peers and history; then dig into drivers and cash flow. Don't optimise one ratio at the expense of others or treat ratios as the cause of value. Ratios are summary statistics; they can be gamed and they lag. Pair them with cash flow and quality of earnings for decisions.
Further Reading
01
Book
The foundational text on using financial statements and ratios for investment analysis. The discipline of comparing ratios across time and peers starts here.
02
Book
Practical guide to ratio analysis, adjustments, and red flags. Covers how to interpret and when to distrust ratios.
03
Book
Short, focused treatment of what key ratios mean and how to use them. Good first pass for the ratio toolkit.
Why this matters next
mental modelsMargin of Safety
Financial Ratios applied the Margin of Safety mental model
mental modelsLeverage
Financial Ratios applied the Leverage mental model
mental modelsScale
Financial Ratios applied the Scale mental model
mental modelsQuality
Financial Ratios applied the Quality mental model
mental modelsCost of Capital
Financial Ratios applied the Cost of Capital mental model
mental modelsCost
Financial Ratios applied the Cost mental model
Frequently asked questions
What is Financial Ratios?
Financial Ratios is a mental model used for better thinking and decision-making.
How do you apply Financial Ratios?
To apply Financial Ratios, identify situations where this framework is relevant, then use it as a lens to evaluate your options and decisions. The model is most useful when combined with other complementary mental models.
What category does Financial Ratios fall under?
Financial Ratios falls under the Finance & Investing category of mental models. Other models in this category can be found on the Finance & Investing hub page.
Why is Financial Ratios important?
Financial Ratios is important because it provides a structured way to think about problems that would otherwise be approached with intuition alone. Understanding this model helps you avoid common reasoning errors and make better decisions.
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