Percentage Change Explained: Salary Raises, Investment Returns, and Inflation

Whether you are negotiating a salary raise, tracking your investment portfolio, or trying to understand why your grocery bill keeps climbing, percentage change is the single most useful mathematical concept in personal finance. Yet most people have only a vague understanding of how it actually works.

This guide explains the percentage change formula in plain language, walks through real-world examples in salary, investments, and inflation, and highlights the common mistakes that lead to misunderstanding financial news.

The Percentage Change Formula

Percentage change measures how much a value has moved relative to its starting point. The formula is:

A positive result is an increase; a negative result is a decrease.

Example: Your salary increases from €3,200 to €3,520 per month.
Change = [(3520 − 3200) ÷ 3200] × 100 = [320 ÷ 3200] × 100 = 10% increase.

Salary Negotiations: What a Percentage Raise Really Means

When an employer offers you a "5% raise," it sounds significant. But the actual monetary value depends entirely on your current salary. Here is a reference table:

• €2,000/month + 5% = €100 more per month (€1,200/year)
• €3,500/month + 5% = €175 more per month (€2,100/year)
• €5,000/month + 5% = €250 more per month (€3,000/year)

Key insight: A raise below the inflation rate is actually a pay cut in real terms. If inflation is running at 4% and you receive a 3% raise, your purchasing power has decreased by approximately 1%. Always compare your raise to the current inflation rate.

When negotiating, it is often more effective to anchor on a specific monetary amount rather than a percentage. "I am looking for an increase of €400 per month" is clearer and harder to deflect than "I am looking for a 12% raise."

Investment Returns: Simple Return vs CAGR

Investment returns are almost always expressed as percentages, but there are two very different ways to measure them.

Simple Percentage Return

If you invest €10,000 and it grows to €14,500 over 5 years, your simple return is: [(14,500 − 10,000) ÷ 10,000] × 100 = 45%.

Compound Annual Growth Rate (CAGR)

CAGR tells you the equivalent annual growth rate that would produce the same result:

For the same example: CAGR = [(14,500 ÷ 10,000)^(1/5) − 1] × 100 ≈ 7.7% per year.

CAGR is more useful for comparing investments over different time periods. A fund that returned 80% over 10 years (CAGR ~6.1%) is not necessarily better than one that returned 45% over 5 years (CAGR ~7.7%).

Inflation: The Silent Percentage That Erodes Wealth

Inflation is the rate at which the general price level rises, expressed as a percentage. When inflation is 3%, something that costs €100 today will cost €103 in one year. The compounding effect over time is significant:

• 3% inflation for 10 years: €100 becomes €134 (34% more expensive)
• 3% inflation for 20 years: €100 becomes €181 (81% more expensive)
• 5% inflation for 10 years: €100 becomes €163 (63% more expensive)

The Rule of 72: Divide 72 by the inflation rate to find roughly how many years it takes for prices to double. At 3% inflation: 72 ÷ 3 = 24 years. At 6%: 72 ÷ 6 = 12 years.

This is why keeping all your savings in a bank account earning 1% interest when inflation is 3% means your real purchasing power is shrinking by approximately 2% per year.