The Price-to-Earnings (P/E) ratio is one of the most widely used valuation metrics. It is calculated as:

$\text{P/E Ratio} = \frac{\text{Current Share Price}}{\text{Earnings Per Share (EPS)}}$

Earnings Per Share (EPS) is typically the trailing twelve months (TTM) earnings. A high P/E can indicate that a stock is overvalued, or that investors have high growth expectations. Conversely, a low P/E might suggest the stock is undervalued or that the company faces significant risks. It's crucial to compare a company's P/E ratio to its historical P/E, the P/E of its industry peers, and the broader market P/E.

The Price-to-Book (P/B) ratio, also known as the market-to-book ratio, is calculated as:

$\text{P/B Ratio} = \frac{\text{Current Share Price}}{\text{Book Value Per Share}}$

Book value per share is derived from the company's balance sheet:

$\text{Book Value Per Share} = \frac{\text{Total Assets} - \text{Total Liabilities}}{\text{Number of Outstanding Shares}}$

This ratio is particularly useful for valuing companies with significant tangible assets, such as banks or manufacturing firms. A P/B ratio below 1 suggests that the market values the company at less than its net asset value, which could indicate an undervalued stock. However, it's less relevant for companies with substantial intangible assets like technology or service firms.

The Price-to-Sales (P/S) ratio is calculated as:

$\text{P/S Ratio} = \frac{\text{Current Share Price}}{\text{Revenue Per Share}}$

Revenue per share is derived from the company's income statement:

$\text{Revenue Per Share} = \frac{\text{Total Revenue}}{\text{Number of Outstanding Shares}}$

This ratio is valuable for comparing companies that may have different accounting practices or are in early stages of growth where earnings might be negative or volatile. It's often used for companies that are not yet profitable, as it focuses on the top line (revenue). A lower P/S ratio compared to industry averages may suggest undervaluation.

The Enterprise Value to EBITDA (EV/EBITDA) ratio is calculated as:

$\text{EV/EBITDA} = \frac{\text{Enterprise Value}}{\text{EBITDA}}$

Enterprise Value (EV) is calculated as:

$\text{Enterprise Value} = \text{Market Capitalization} + \text{Total Debt} - \text{Cash and Cash Equivalents}$

EBITDA (Earnings Before Interest, Taxes, Depreciation, and Amortization) is a measure of a firm's operating performance. EV/EBITDA is favored because it is capital structure-neutral and tax-neutral, making it useful for comparing companies with different debt levels and tax rates. It's a common metric in M&A and for valuing companies across different industries.

The Dividend Yield is calculated as:

$\text{Dividend Yield} = \frac{\text{Annual Dividend Per Share}}{\text{Current Share Price}}$

This ratio is particularly important for investors seeking regular income from their investments. It represents the return an investor receives in the form of dividends for every dollar invested in the stock. While a high dividend yield can be attractive, it's important to also consider the sustainability of the dividend and the company's overall financial health.