CPI Inflation Rate Calculator
From the current and previous Consumer Price Index, compute the inflation rate: (CPI_now - CPI_prev) / CPI_prev x 100%.
Input Data
Results
At a glance:Inflation rate = (current CPI - previous CPI) / previous CPI x 100%. CPI tracks a weighted basket of consumer goods/services; the rate shows how much overall prices rose (positive) or fell (negative = deflation). Example: 110 vs 104 → ≈5.77%. Inflation erodes purchasing power; real return ≈ nominal - inflation. WARNING: CPI is an average basket; personal inflation differs by spending mix; compare on same base/period. Education, not advice.
Formula
Inflation rate = (current CPI − previous CPI) / previous CPI × 100%.
$$Inflation rate: $Inflation = dfrac{CPI_{t}-CPI_{t-1}}{CPI_{t-1}} imes100%$$$$$Example: $dfrac{110-104}{104} imes100%approx5.77%$$$$$A negative value indicates deflation (falling prices).$$How to Use
- Enter the current period's CPI.
- Enter the previous period's CPI.
- View the inflation rate (positive = inflation, negative = deflation).
FAQ
What is CPI and how does it measure inflation?
The CPI is an index tracking a weighted basket of representative consumer goods and services over time. Statistical offices survey household spending to set category weights (food, housing, transport, etc.), then track prices monthly and index them (base = 100). The inflation rate is the percentage change between two index values. The basket-average avoids single-item noise but also means personal experience may differ.
How does inflation relate to real return?
Inflation determines your real (purchasing-power) return. Approx: real return ≈ nominal return - inflation (precisely via Fisher: (1+nominal)/(1+inflation)-1). If a deposit yields 4% but inflation is 5.77%, real return ≈ -1.77% — you lose purchasing power. This is why high inflation makes low-interest deposits 'lose money' and why you should look at real, not nominal, returns.
Is inflation always bad? What about deflation?
Moderate, stable inflation (~2% target for many central banks) is healthy — it encourages spending/investment and eases debt burdens. High/uncontrolled inflation erodes savings and distorts prices. Deflation (falling prices) sounds good but risks a deflationary spiral: delayed consumption → weaker demand → job cuts → less demand. Central banks target low, stable positive inflation, not zero.
Where do I find Hong Kong inflation data? What is Composite CPI?
In Hong Kong, the Census and Statistics Department compiles the Composite CPI — a basket of everyday goods/services weighted by household spending, compared across periods to derive the inflation rate. It also publishes Class A/B/C CPI for lower/middle/higher-spending households, and 'underlying inflation' strips out one-off government relief. For authoritative figures, visit the C&SD website.
Why does inflation feel higher than the official rate?
Because everyone's basket differs from the average, plus psychological and frequency biases. If you spend heavily on fast-rising items (rent, dining), your personal inflation exceeds the composite. High-frequency purchases amplify the feeling; one-off subsidies lower the official figure you may not feel. Check the CPI class closest to your spending, or track your own basket.
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References
Content review: Calculatorism Finance Team. Results are for reference only; please refer to the relevant authorities for the official figures.