P/E and P/B Ratios: How to Value a Stock

The P/E ratio compares a company’s share price with its earnings per share. The P/B ratio compares the share price with the company’s book value per share.

Both ratios can help you understand valuation, but neither can tell you by itself whether a stock is worth buying.

A low P/E can signal undervaluation or a troubled business. A high P/E can signal strong growth expectations or excessive optimism.

What Is the P/E Ratio?

P/E means price-to-earnings ratio.

The formula is:

P/E = Market price per share ÷ Earnings per share

Suppose:

• Share price = ₹500
• EPS = ₹25

Then:

P/E = ₹500 ÷ ₹25 = 20

Investors are paying ₹20 for each ₹1 of current annual earnings.

What Is EPS?

EPS means earnings per share.

A simplified formula is:

EPS = Profit attributable to equity shareholders ÷ Weighted average number of shares

EPS is important because the P/E ratio uses earnings on a per-share basis.

What Does a P/E of 20 Mean?

A P/E of 20 does not mean it will take exactly 20 years to recover your investment.

That interpretation ignores:

• Earnings growth
• Dividends
• Changes in valuation
• Business risk
• Future profitability

P/E is a valuation multiple, not a guaranteed payback period.

What Does a High P/E Mean?

A high P/E can mean investors expect:

• Fast growth
• High profitability
• Strong competitive advantage
• Predictable earnings
• Excellent management

It can also mean the stock is overpriced.

The correct interpretation depends on future earnings.

What Does a Low P/E Mean?

A low P/E may indicate:

• Undervaluation
• Low expected growth
• Cyclical peak profits
• High debt
• Governance concerns
• Business decline

This is why buying “the five lowest-P/E stocks” is not a complete investment strategy.

What Is Trailing P/E?

Trailing P/E uses historical reported earnings.

Its advantage is that the earnings have already occurred.

Its weakness is that the future may look very different.

What Is Forward P/E?

Forward P/E uses expected future earnings.

It can be useful when profits are changing quickly.

But estimates can be wrong.

Analysts may revise future earnings downward, making a seemingly cheap forward P/E much less attractive.

What Is the P/B Ratio?

P/B means price-to-book ratio.

Formula:

P/B = Market price per share ÷ Book value per share

Suppose:

• Share price = ₹300
• Book value per share = ₹150

Then:

P/B = 2

The stock trades at twice its accounting book value per share.

What Is Book Value?

Book value broadly relates to shareholders’ equity recorded on the balance sheet.

It reflects accounting values, which may differ significantly from economic value.

A brand, software platform, distribution network, or intellectual property may create value that is not fully reflected in traditional book assets.

When Is P/B Useful?

P/B can be more useful in asset-heavy or balance-sheet-driven industries.

It is commonly considered when analysing financial businesses such as banks, although investors also need to examine:

• Asset quality
• Return on equity
• Loan growth
• Capital adequacy
• Credit costs

A low P/B bank can be cheap because investors expect future losses.

When Is P/B Less Useful?

P/B can be less informative for:

• Software firms
• Consumer brands
• Platform businesses
• Asset-light companies

These businesses can generate large profits without requiring large accounting book value.

Why ROE Matters With P/B

Return on equity helps explain how effectively a company uses shareholder capital.

A company consistently earning high ROE may deserve a higher P/B multiple than a competitor earning poor returns.

For example:

Company A:

• P/B = 4
• ROE = 25%

Company B:

• P/B = 1
• ROE = 5%

Company B is not automatically the better bargain.

Compare P/E With Growth

Suppose:

Company X:

• P/E = 15
• Earnings growth = 3%

Company Y:

• P/E = 30
• Earnings growth = 25%

The lower-P/E company may not necessarily be more attractive.

Investors pay for future cash flows, not only current earnings.

What Is the PEG Ratio?

The PEG ratio relates P/E to earnings growth.

A simplified version is:

PEG = P/E ÷ Earnings growth rate

It can add context but should not be used mechanically.

Growth estimates are uncertain, and business quality is not fully captured.

What Is a Value Trap?

A value trap is a stock that looks statistically cheap but remains cheap or falls because the business deteriorates.

Examples of causes include:

• Falling demand
• Excess debt
• Technology disruption
• Poor capital allocation
• Governance problems

Low valuation is only useful when future business economics remain sound.

What Is a Cyclical P/E Trap?

Commodity and cyclical businesses can look cheapest near peak earnings.

Suppose a steel company’s profit temporarily surges because steel prices are unusually high.

The P/E may fall dramatically.

If profits later normalise, the P/E based on peak earnings was misleading.

Investors should use normalised earnings where appropriate.

Can P/E Be Negative?

When a company reports losses, the conventional P/E ratio becomes meaningless or is often shown as unavailable.

You cannot sensibly interpret a negative-EPS business using a normal P/E framework.

Other valuation measures may be needed.

Should You Compare P/E Across Industries?

Usually not without context.

A bank, software firm, steel producer, and consumer-goods company can deserve very different valuation ranges.

Compare:

• Similar business models
• Similar growth
• Similar capital intensity
• Similar risk

Historical P/E vs Peer P/E

Two useful comparisons are:

Historical Valuation

Is the company trading above or below its own normal range?

Peer Valuation

How does it compare with similar companies?

Neither tells the whole story.

A company may deserve a permanently lower valuation after its competitive position weakens.

What Else Should You Check Before Buying?

Revenue Growth

Are sales expanding sustainably?

Profit Growth

Are earnings improving without accounting distortions?

Cash Flow

Do reported profits translate into cash?

Debt

Can the company comfortably service its obligations?

ROE and ROCE

Is management earning attractive returns on capital?

Governance

Do shareholders trust management and capital allocation?

Competitive Advantage

Can the business defend margins over time?

Simple Stock Valuation Checklist

Before buying, ask:

1. What does the company actually do?
2. How does it earn money?
3. Is revenue growing?
4. Are margins stable?
5. Is debt manageable?
6. Is cash flow healthy?
7. What is the current P/E?
8. How does it compare with history and peers?
9. What growth is already priced in?
10. What could go wrong?

Common P/E and P/B Mistakes

Avoid:

• Buying solely because P/E is low
• Assuming high P/E means bad stock
• Comparing unrelated sectors
• Ignoring debt
• Using peak cyclical earnings
• Trusting forward estimates blindly
• Ignoring return on equity when interpreting P/B

FAQs

Key Takeaways

• P/E compares share price with earnings.
• P/B compares share price with book value.
• Low valuation does not automatically mean cheap.
• High valuation does not automatically mean expensive.
• Compare similar companies and historical ranges.
• Use growth, ROE, debt, cash flow, and business quality alongside valuation multiples.