Data Note
Disinflation describes slower price increases, not a return to an earlier price level. Index calculations distinguish falling annual inflation, outright deflation and the continuing cumulative change in household purchasing requirements.
A falling inflation rate means that prices are rising more slowly when the rate remains positive. It does not mean that the price level has returned to an earlier value. Confusing the rate of increase with the accumulated level can obscure both the progress of disinflation and the price burden households continue to face.
The Central Bank of the Republic of Türkiye defines disinflation in its glossary as a decline in the rate of price increase. It distinguishes this from deflation, a sustained decline in the general price level. The examples below explain those definitions without using current Turkish inflation observations or implying a forecast.
Start with a hypothetical price index of 100. Let prices rise by 60 percent in the first year, 20 percent in the second and 10 percent in the third.
| Hypothetical year | Annual inflation | Year-end index |
|---|---|---|
| Initial position | — | 100.0 |
| Year 1 | 60% | 160.0 |
| Year 2 | 20% | 192.0 |
| Year 3 | 10% | 211.2 |
Inflation declines sharply across the three years, yet the index more than doubles. The cumulative increase is 111.2 percent, obtained from 1.6 × 1.2 × 1.1 − 1. Adding the annual rates would give 90 percent and ignore compounding.
Returning the index from 211.2 to 100 would require a price decline of approximately 52.65 percent. A future inflation rate of zero would instead leave the index at 211.2. Price stability at the new level and restoration of the old level are different outcomes.
In a separate hypothetical illustration, an index was 100 in a particular month last year and 110 in the following month. This year it is 132 and then 133.1 in the corresponding months.
The twelve-month rate falls from 32 percent to 21 percent. But the current index rises from 132 to 133.1, an increase of approximately 0.83 percent. The large earlier monthly rise has entered the comparison base. The annual slowdown does not erase the current increase.
An assessment of recent momentum should therefore examine an appropriate sequence of monthly observations as well as the annual rate, retaining the seasonal-adjustment convention. One favorable annual comparison cannot establish the future path of prices, just as a single strong monthly observation cannot determine the full annual outcome.
Suppose nominal income starts at 100 and reaches 150 by the third year of the first example. Deflating by the price-index relative of 2.112 gives purchasing power equivalent to about 71.02 in initial-period units. Nominal income has increased, but it has not matched the cumulative price increase in that scenario.
This example does not describe the experience of a particular Turkish household. Actual consumption baskets, income sources and timing differ. Nor does an aggregate inflation rate imply that every individual price rises at the same speed. Changes in relative prices remain part of the household's experience.
Contract decisions need the same distinction. A price escalation clause tied to annual inflation may produce a smaller increase during disinflation while still raising the amount paid. Evaluating affordability requires the resulting payment level and the income available when it is due. A lower adjustment rate alone does not establish a lower cash obligation.
A clear disinflation assessment consequently reports the observation interval, the inflation rate and the cumulative price level separately. Where household affordability is discussed, it also examines income and the relevant spending basket. Those distinctions allow slower inflation to be recognized accurately while avoiding an unsupported claim that earlier price increases have been reversed.