How to calculate your personal inflation rate step by step
The official CPI doesn't exactly reflect your situation. Learn to calculate your own inflation rate based on your real expenses.
The official CPI is an average that reflects the spending habits of a typical household. But your personal inflation rate can be very different — especially if you rent in a major city, own a car, or eat out regularly.
Why your inflation may differ from the CPI
National statistics offices calculate the CPI by weighting different spending categories according to average household consumption. If your spending distribution differs from that average, your personal inflation will be different.
For example: housing has a weight of around 13% in the general CPI, but if you spend 40% of your income on rent and rents rise 10%, that component contributes 4% to your inflation — far more than it does to the average CPI.
Step 1: Identify your spending categories
Break down your monthly expenses into these main categories:
- Housing (rent or mortgage, utilities)
- Groceries
- Eating out (cafés, restaurants, takeaways)
- Transport (car, public transport, fuel)
- Leisure and culture
- Health
- Education
- Clothing and footwear
- Communications (mobile, broadband)
- Other
Step 2: Calculate each category’s weight
Divide the monthly spend on each category by your total monthly spend:
Housing_weight = Housing_spend / Total_spend × 100Example: if you spend £900 on rent out of a total £2,200, housing weighs 40.9%.
Step 3: Apply the price change for each category
Statistics offices publish monthly CPI changes by group. Multiply each weight by its category’s change:
Personal inflation = Σ (category_weight × CPI_category_change) / 100Practical example
| Category | Weight | CPI category change | Contribution |
|---|---|---|---|
| Housing | 40% | +10% | +4.0% |
| Groceries | 25% | +6% | +1.5% |
| Transport | 15% | +4% | +0.6% |
| Other | 20% | +3% | +0.6% |
| Total | +6.7% |
If the general CPI that year was 5%, your personal inflation would be 6.7% — nearly two percentage points higher.
Where to find CPI data by category
The ONS (UK), INE (Spain), INSEE (France) and Destatis (Germany) all publish monthly CPI breakdowns by category on their websites.
Use our inflation calculator to apply historical CPI to any amount and period.