How do you learn the price-to-earnings ratio quickly and correctly? Start by separating what investors pay for a share from the earnings the business reports for each share. The price-to-earnings ratio, usually called the P/E ratio, compares a share price with earnings per share. It gives an initial way to think about how much the market is paying relative to measured profits, but it cannot prove whether an investment is good or bad. This eduKateSG Finance Quick Notes lesson teaches the formula, a S$24 example and the questions that make a valuation comparison honest and useful.
- P/E ratio: share price divided by earnings per share, usually expressed as ‘times’ or ‘x’.
- EPS: earnings per share, calculated using relevant earnings and share-count conventions.
- Example: S$24 share price ÷ S$2 EPS = 12 times earnings.
- Trailing P/E: uses historical earnings, often the most recent twelve months.
- Forward P/E: uses estimated future earnings that might not materialise.
- Interpret with care: lower P/E does not automatically mean better value.
- Check profits: company debt, cash flow, growth expectations and unusual gains all matter.
Teaching paragraph 1 — learn to divide two amounts that belong together. Imagine a fictional listed company whose shares trade at S$24 each. Suppose its earnings per share for the relevant twelve-month period are S$2. The price-to-earnings calculation is S$24 ÷ S$2 = 12, usually written as a P/E of 12×. The units cancel because a share price and earnings per share are both monetary amounts per share. The calculation tells you that the market price is twelve times the selected annual EPS figure. It does not say earnings will stay constant or that you will receive twelve years of guaranteed payments.
Teaching paragraph 2 — understand where earnings per share come from. Imagine the same fictional company earned S$20 million attributable to ordinary shareholders for the relevant period, and the appropriate weighted-average number of ordinary shares for this simplified calculation is 10 million. The approximate basic EPS is S$20 million ÷ 10 million = S$2 per share. Different share classes, instruments convertible into shares and accounting adjustments may change reported or diluted EPS in real company accounts. Use the company’s disclosed measure, report period and calculation basis rather than inventing your own share count.
Teaching paragraph 3 — test what happens when the price changes but EPS does not. Suppose the market price falls from S$24 to S$20 while the historical EPS used in the calculation remains S$2. The P/E becomes S$20 ÷ S$2 = 10×. The lower ratio might be attractive to some investors, but it might also reflect serious worries about future earnings. If those earnings subsequently fall, the P/E can rise again without the share price increasing. Learn to ask why the price or profit figure changed, not merely whether the P/E is numerically small.
The P/E Formula
P/E ratio = price per share ÷ earnings per share. At S$24 price and S$2 EPS, the result is 12×. You can also express the same simple relationship as market capitalisation divided by annual earnings attributable to ordinary shareholders, if the share counts and measurement bases are consistent. This equivalence is useful for checking calculations, but real accounts can involve preferred shares, differing share counts or alternative earnings measures.
A Worked S$24 Example
- Fictional company’s annual earnings attributable to ordinary shares: S$20 million.
- Simplified weighted-average ordinary share count: 10 million shares.
- Earnings per share: S$2.
- Current market price per share: S$24.
- P/E: 24 ÷ 2 = 12×.
- If price falls to S$20 and EPS used stays S$2: 10×.
- If price remains S$24 but EPS declines to S$1.50: 16×.
The last example teaches why a rising P/E is not always evidence that investors have become more optimistic. Sometimes the denominator—earnings—has fallen. Conversely, a share price may rise while a business’s earnings rise faster, causing the P/E to fall. Always look at both inputs and the dates attached to them.
What Is Earnings Per Share?
Earnings per share is a company’s earnings allocated to a share under the relevant reporting method. In a basic illustration, divide relevant earnings by the weighted-average ordinary share count. Real company reports distinguish basic from diluted EPS and may present continuing-operations and other measures. Weighted averages matter when shares were issued or repurchased during the period. A number from an advertising screenshot is not a substitute for the reported calculation.
Trailing P/E Versus Forward P/E
A trailing P/E uses historical earnings, often those reported for the most recent twelve months. A forward P/E uses estimated earnings for a future period. Historical earnings are known but may be unrepresentative; future estimates may capture anticipated growth but can be wrong. Comparing a historical P/E from Company A with a forward P/E from Company B without labelling them can mislead readers. A good comparison uses the same type of earnings, the same length of time and transparent assumptions.
Why a Low P/E Can Be a Trap
Imagine Company A trades at 6× historical earnings while Company B trades at 15×. It may appear that A is cheaper, but suppose A faces declining demand, unsustainable profits or significant obligations. Its apparently low ratio may reflect real concerns. Company B may have more reliable earnings or better growth prospects, although that does not automatically make it a good purchase. Valuation requires understanding risk, the quality of earnings and what is already reflected in the share price. A single ratio cannot settle the decision.
Why a High P/E Is Not Automatically Wrong
Some businesses trade at high multiples because investors expect profits to grow substantially in the future. But growth might be slower than expected, and a high price leaves less room for disappointing results. A high P/E can therefore represent optimistic expectations, not necessarily a mathematical error. Compare expected growth against realistic evidence, rather than declaring that every high ratio is either a bargain or a bubble.
What If Earnings Are Zero or Negative?
If EPS is zero, the standard P/E division is undefined. If EPS is negative, a mechanical calculation produces a negative number, but many financial platforms display P/E as ‘N/M’, meaning not meaningful, instead. A negative P/E should not be interpreted as the company being incredibly cheap. It may simply be loss-making. The right beginner response is to investigate the losses, cash position, business risks and other valuation measures rather than trying to force a normal positive-earnings interpretation.
One-Off Profits Can Distort a P/E
Suppose a company sells a major property and reports a large gain in one year. The profit figure may jump even if ordinary operations did not improve. A trailing P/E based on that unusually large earnings figure may look deceptively low. Conversely, a one-time impairment or restructuring charge can reduce earnings temporarily and make a ratio look very high. Read the financial statement notes and determine what is recurring or exceptional. Do not remove items selectively just to make a company look attractive.
P/E Is Not the Same as Dividend Yield
P/E compares share price with earnings per share. Dividend yield compares annual dividends per share with share price. Earnings are not necessarily paid out as dividends: the company can retain profits, reinvest them or use cash for other obligations. A company may report high earnings and pay no dividend. Another may pay a large distribution despite pressures elsewhere in the business. These ratios answer different questions and should not be substituted for each other. Read How to Learn Dividend Yield Quickly and Correctly for the second formula.
P/E Is Not the Same as a Guaranteed Payback Time
It is tempting to say that 12× earnings means an investor will ‘get the money back in twelve years’. That is not how owning an ordinary share works. Earnings may change, may not be paid as cash dividends, and do not automatically flow to shareholders in equal annual instalments. The share price may move for many reasons, and shares may be sold or held indefinitely. Treat the P/E as a market valuation multiple, not a repayment schedule.
Why Debt and Cash Flow Still Matter
Two firms with identical P/E ratios may have very different debts, capital requirements and cash flows. A heavily indebted business may face refinancing pressure even while its accounting profits look respectable. A rapidly growing company may report earnings but need large amounts of cash for expansion. Look at its balance sheet, operating cash flow, capital spending and the reliability of its revenue. A ratio is most useful when it helps you ask more informed questions about the underlying business.
How to Make Comparisons Fairer
- Use EPS measures calculated on a comparable accounting basis.
- Match historical periods or clearly label forward estimates.
- Compare businesses with relevant similarities, not just any two stock tickers.
- Check unusual one-time gains and losses.
- Review debt, cash flow, earnings trends and business risks.
- Check whether share issuance or buybacks changed the EPS denominator.
- Ask why the market may be assigning different prices to their earnings.
Common Mistakes
- Calling a low P/E proof that a share must rise.
- Treating forward earnings estimates as reported fact.
- Comparing a trailing P/E with a forecast P/E without saying so.
- Using current share price and mismatched share or earnings data.
- Misreading negative earnings and a negative numerical ratio as a bargain.
- Equating annual accounting earnings with a guaranteed dividend payout.
- Ignoring the company’s debt and quality of cash generation.
Ten-Minute P/E Practice
- Minutes 1–2: explain price, earnings and EPS using one simple sentence each.
- Minutes 3–4: calculate EPS for S$12 million of relevant earnings and 6 million shares.
- Minutes 5–6: calculate P/E at a hypothetical share price of S$18.
- Minutes 7–8: change the price to S$15 and calculate again.
- Minutes 9–10: list two reasons the lower P/E might not represent a better investment.
Mini Quiz and Answers
Question 1: What is EPS on S$12 million earnings and 6 million appropriate shares in the simplified model? Answer: S$2 per share.
Question 2: At a S$18 share price and S$2 EPS, what is P/E? Answer: 9×.
Question 3: If the company suddenly reports a loss, is the ordinary positive-earnings P/E still straightforward to interpret? Answer: No. The ratio can become undefined or not meaningful under the usual convention.
Continue Your Finance Quick Notes
Start with How to Learn Stocks Quickly and Correctly to understand the share itself, then How to Learn Market Capitalisation Quickly and Correctly to measure a company’s quoted equity value. Read How to Learn Dividend Yield Quickly and Correctly for distributions and How to Learn Investment Risk and Diversification Quickly and Correctly for the possibility of losses.
Trusted Reading and Key Idea
See the official Investor.gov P/E definition and MoneySense guide to assessing shares. These Quick Notes are general educational explanations and not valuation advice about any particular company. Remember: price divided by earnings is a useful question, not a final investment answer.