Reading time: 5 minutes · Published: Jun 2025

TL;DR: CPI measures a fixed basket of consumer prices. M3 measures the total rands in the economy. They answer different questions. CPI tells you about shopping costs. M3 tells you about monetary dilution - and often shows a bigger gap between your money and your wealth.

M3 vs CPI: Which Measure Should You Trust?

If you follow South African economic news, you have seen the CPI inflation rate reported every month. But there is another number that often tells a different story: M3 money supply growth.

What CPI Actually Measures

The Consumer Price Index (CPI) tracks the price of a fixed basket of goods and services over time. Stats SA determines the basket, updates the weights periodically, and publishes a headline inflation rate. It is useful for:

Understanding how consumer prices are changing
SARB interest rate decisions (CPI targeting)
Cost-of-living adjustments in salaries and grants

But CPI has limitations. It uses substitution effects, quality adjustments, and averaging. Your personal inflation - what you actually pay for rent, school fees, medical aid, transport, and food - can be very different from the headline number.

What M3 Money Supply Actually Measures

M3 is the total quantity of rands in the economy. It includes cash, bank deposits, and other liquid assets. It is not a price index. It is a quantity index. When M3 grows, there are simply more rands.

M3 is useful for:

Understanding monetary dilution - the expansion of the rand pool
Benchmarking whether your income or savings are keeping pace with money creation
Seeing long-term trends that CPI may smooth over

Why They Diverge

CPI and M3 often move at different rates. M3 tends to grow faster than CPI over long periods in South Africa. The gap represents money that is created but has not yet pushed up consumer prices - or that flows into assets, property, and financial markets instead.

Comparison chart showing M3 money supply growth versus CPI inflation in South Africa, indexed to 100. M3 rises faster than CPI, showing the gap between money creation and consumer price inflation.

M3 Money Supply (blue) vs CPI Inflation Index (red), both indexed to 100 at the starting period. The widening gap shows monetary dilution that CPI does not capture.

Why this matters: If CPI says 5% and M3 says 10%, and your salary rose by 7%, you beat CPI but fell behind M3. Which benchmark you choose changes whether you think you are ahead or behind.

Which One Should You Use?

The honest answer: both. They answer different questions.

Use CPI for short-term cost-of-living adjustments and budgeting.
Use M3 for long-term wealth, savings, salary, and asset comparisons.

If you only look at CPI, you may think you are doing fine when your purchasing power is quietly eroding. If you only look at M3, you may overestimate the immediate impact on your monthly budget. Together, they give a fuller picture.

View the interactive M3 vs CPI chart to see the comparison over time, or use the calculator to check specific amounts and dates.