Cumulative Inflation Calculator (Total Inflation from Monthly Rates)
Compounds 1–12 monthly inflation rates into cumulative inflation, the average monthly and annualised rate and the inflation-adjusted value of an amount.
Things to keep in mind:
- Official cumulative inflation is calculated from TÜİK index values; because monthly rates are published rounded, the result can differ from the official figure by a few thousandths.
- Rent caps, revaluation rates and tax updates can be based on different indices and periods; use the rate announced by the responsible institution for official purposes.
- The annualised rate is a projection that assumes the recent pace lasts a year, not a forecast.
Calculator
Result
Enter the values and press Calculate to see the result here.
About this tool
Adding up monthly inflation rates does not give cumulative inflation, because each month's increase applies to prices that already rose the month before. The correct method is to compound the rates. When updating a salary, a rent or a receivable, "how much inflation was there in the last six months?" is answered by this calculation.
Formulas
With monthly rates a₁, a₂, …, aₙ (%) and n months:
- Compound factor = (1 + a₁/100) × (1 + a₂/100) × … × (1 + aₙ/100)
- Cumulative inflation (%) = (factor − 1) × 100
- Average monthly inflation (%) = (factor^(1/n) − 1) × 100 (geometric mean)
- Annualised inflation (%) = (factor^(12/n) − 1) × 100
- Inflation-adjusted amount = amount × factor; purchasing power = amount ÷ factor
- Loss of purchasing power (%) = (1 − 1 ÷ factor) × 100
Example
Let three monthly rates be 2.5%, 3% and 1.5%. The simple sum is 7%, but the correct result is 1.025 × 1.03 × 1.015 = 1.0716 → 7.16% cumulative inflation. The average monthly rate is 1.0716^(1/3) − 1 = 2.33%; if this pace lasted a year, annual inflation would be 31.86%.
How to read the result
The cumulative rate shows how much a price at the start of the period has risen by its end: a basket of 10,000 TL rises to 14,211.43 TL with 42.11% cumulative inflation, and the same 10,000 TL is worth only 7,036.59 TL of start-of-period purchasing power at the end. The "annual inflation" published by TÜİK is the compounded result of the last 12 monthly changes; enter 12 months to verify it (index rounding can cause small differences). Use the inflation-adjusted salary tool to see how your salary changed.
How to use
- Choose the number of months to include (1–12).
- Enter each month's inflation rate in order (e.g. TÜİK's monthly CPI change); negative values are allowed.
- Optionally enter an amount to see its end-of-period value and purchasing power.
- Read the cumulative, average monthly and annualised rates.
Notes
Only the first "month count" months are used; values in later fields are ignored. A month left at zero counts as 0%. The average monthly rate is a geometric mean. Rates and amounts are rounded half-up to 2 decimals; intermediate products are not rounded.
Sources
Frequently asked questions
Each month's increase applies to prices that already rose. The sum of three months at 2.5%, 3% and 1.5% is 7%, while the compounded result is 1.025 × 1.03 × 1.015 − 1 = 7.16%. The gap grows as rates rise.
Take the n-th root of the compound factor: (1.0716)^(1/3) − 1 = 2.33%. This geometric mean is the monthly rate that, applied every month, gives the same total.
Enter the six monthly rates, find the cumulative inflation and compare it with your raise. If the raise is lower, you lose in real terms; the inflation-adjusted salary tool gives the detailed calculation.
Yes. Entering the last 12 monthly CPI changes gives a cumulative rate very close to the published annual inflation. Small differences come from monthly rates being published rounded to two decimals.
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