Measuring inflation: rate, base effect and the vocabulary of price change

Detail

1. What inflation is

• Inflation means the general price level keeps rising over time. "General" means most goods and services, not only one item. "Continuing" means it lasts; it is not a one-time jump.
• Purchasing power of money is the amount of goods one rupee can buy. Inflation lowers it.

• Example: a basket costs ₹100 this year and ₹110 next year. The same ₹100 now buys only about 91% of the basket (100/110).

• When inflation becomes very high, money stops working well (Class 11, Index Numbers):

• It stops being a good medium of exchange (something people accept in payment). Sellers do not want money that loses value quickly.

• It stops being a good unit of account (the measure we use to state prices and keep accounts). Prices change too fast to compare.

• Two main causes:

• Demand-pull (excess demand): total demand is more than what the economy can produce. Example: the government spends with borrowed or newly created money (deficit financing) when factories cannot produce more → too much money chases too few goods → prices rise (Class 12, Determination of Income and Employment).

• Cost-push: costs of production go up (wages, fuel, raw materials) → firms charge higher prices.

• Link with money supply: NCERT's Correlation chapter uses money supply and prices as an example of two variables that move together. This is a correlation. It does not by itself prove that one causes the other.

2. How the inflation rate is calculated

• Price index: one number that shows how prices of a fixed basket have changed compared with a base year (base year index = 100).
• Base year: the reference year when the index is set to 100. For India's new CPI it is 2024 = 100 [2].
• Year-on-year (y-o-y) inflation rate for a monthly index:

Inflation rate (%) = (Iₜ − Iₜ₋₁₂) / Iₜ₋₁₂ × 100

• Iₜ = index for this month. Iₜ₋₁₂ = index for the same month last year.

• MoSPI uses this exact formula for CPI inflation (2026) [2].

• Worked example:

• CPI in June 2025 = 105. CPI in June 2024 = 100.

• Inflation = (105 − 100)/100 × 100 = 5%.

• Why compare with the same month last year? Prices move with the seasons (vegetables are cheap in winter, for example). Comparing June with June removes most of this seasonal effect.

• Who publishes the numbers:
• CPI (Consumer Price Index: retail prices that households pay) is published monthly by MoSPI (Ministry of Statistics and Programme Implementation).
• WPI (Wholesale Price Index: prices in bulk trade) is published monthly by the Office of the Economic Adviser, DPIIT.

• (NCERT outdated: gives a weekly WPI formula, (Xₜ − Xₜ₋₁)/Xₜ₋₁ × 100. WPI is now monthly. It is not weekly any more.)

• How CPI prices are collected now:

• The Field Operations Division of NSS, MoSPI collects prices every month from 1,465 rural and 1,395 urban markets in 434 towns (CPI 2024 series) [2].
• 12 online markets in 12 towns with more than 25 lakh people are covered, and their prices are collected weekly [2].
• Price collectors use tablets (CAPI, Computer Assisted Personal Interview) instead of paper [2].

3. India's new CPI series (base 2024 = 100)

• Released on 12 February 2026, starting with data for January 2026 [2][3].
• Weights (the share of each item in the basket) come from the Household Consumption Expenditure Survey (HCES) 2023-24 [2].
• Weighted items went up from 299 to 358 (goods 259 → 308; services 40 → 50) [2].
• COICOP 2018 (Classification of Individual Consumption According to Purpose, a UN system for grouping household spending) is now used. So India's CPI can be compared with other countries. The new CPI has 12 Divisions, 43 Groups, 92 Classes, 162 Sub-classes [2].
• Formulas used:
• Jevons index (a geometric mean of price changes) for the lowest-level indices [2].

• Young/Modified Laspeyres index (uses fixed base-period weights) for higher-level indices [2].

• Linking factor: a number used to join the old series (2012) and the new series (2024) so we get one long, comparable series.

• LF = Average index of new series ÷ Average index of old series, both for the overlap year 2025 [2].
• Linked old index = Old index × LF. General-level LF (Combined) = 0.5267 [2].

• A linked back series from January 2013 is available [2].

• Future base revisions: MoSPI plans to update the base every 3–5 years, depending on when new HCES data comes out [2].

4. Base effect

• Base effect: y-o-y inflation depends on two things: prices today and prices a year ago. The index level a year ago (the "base") can change this year's inflation rate by itself.
• Low base → high inflation rate:
• Prices were unusually low last year (for example, a vegetable glut).

• The denominator Iₜ₋₁₂ is small → this year's rate looks large.

• High base → low inflation rate:

• Last year saw a price spike.

• The denominator is large → this year's rate looks small, even if prices are still rising now.

• Momentum and base effect (RBI method):

• Momentum = the month-on-month (m-o-m) price change in the current month.
• Base effect = the m-o-m price change in the same month a year ago. This change now "drops out" of the 12-month window [4].

• Change in y-o-y inflation ≈ Momentum now − Momentum a year ago (base effect).

• Worked example (high base):

• Index: June 2024 = 100, July 2024 = 104 (a spike of +4% in one month). June 2025 = 105, July 2025 = 105.5.
• June 2025 inflation = 5%. July 2025 inflation = (105.5 − 104)/104 × 100 ≈ 1.44%.
• Momentum in July 2025 = +0.48%. Base effect = +4% dropping out. 0.48 − 4 ≈ −3.5 points. So inflation fell from 5% to about 1.4%.

• Prices still rose, but the headline rate fell sharply. This is a favourable base effect.

• Worked example (low base): if July 2024 had instead fallen to 98, then July 2025 inflation = (105.5 − 98)/98 × 100 ≈ 7.65%. The same price today gives a much higher rate.

• RBI uses this in practice:
• In the May 2021 inflation jump, RBI said high momentum across food, fuel and core items, together with an unfavourable base effect, pushed headline inflation up [4].

• In September 2024, inflation rose again after two months below target. RBI said an adverse statistical base effect was made worse by a new rise in food price momentum [5].

• Why it matters for policy: RBI tries to "look through" rises that come only from the base. It does not raise rates for them. It watches momentum closely, because momentum shows the real price pressure now.

5. Inflation target: the benchmark for these numbers

• Section 45ZA of the RBI Act: the Central Government, in consultation with the RBI, sets the inflation target in terms of CPI once every five years [8].
• Target notified on 5 August 2016: 4% CPI inflation, with an upper tolerance of 6% and a lower tolerance of 2%, for 5 August 2016 to 31 March 2021 [8].
• The target was kept at 4% (2–6%) for the next five years, up to March 2026. RBI released a Discussion Paper on Review of the Monetary Policy Framework on 21 August 2025 before the next target period [9]. (Verify the target notified for 2026–31.)

6. Food inflation

• Food inflation: the y-o-y rise in food prices. MoSPI measures it with the CFPI (Consumer Food Price Index).
• Food has a large weight in CPI, so it drives headline inflation.
• CPI 2012 (Combined): Food and Beverages = 45.86% (NCERT: about 46%) [2].
• CPI 2024 (Combined): 36.75% under the new COICOP structure. Under the old classification it would be 40.10% [2].
• Rural weight is higher than urban: under the old structure, rural 54.18% (2012) → 44.80% (2024); urban 36.29% → 34.26% [2].

• Reason for the fall: as incomes rise, households spend a smaller share on food. This is Engel's law.

• Worked example (effect of weight):

• Suppose food inflation = 10% and non-food inflation = 3%.
• With the 2012 weight: 0.4586 × 10 + 0.5414 × 3 ≈ 6.2% headline.
• With the 2024 weight: 0.3675 × 10 + 0.6325 × 3 ≈ 5.6% headline.

• The same food shock now moves headline CPI less.

• Recent data: CFPI food inflation was 2.13% in January 2026 (provisional; rural 1.96%, urban 2.44%) [3].

• Why food prices are volatile (they swing up and down a lot):
• Supply depends on the monsoon. Heatwaves and unseasonal rain can destroy crops quickly.

• TOP (tomato, onion, potato) are perishable and India has thin storage for them, so a small supply loss causes a big price jump.

• Policy response to TOP volatility:

• Operation Greens was announced in the Union Budget 2018-19 with ₹500 crore, modelled on Operation Flood. It was launched by the Ministry of Food Processing Industries (MoFPI) in November 2018 [6].
• It gives a 50% subsidy on transport and storage in the short term. In the long term it gives grants of 35–70% of project cost (up to ₹50 crore per project) for value-addition projects [6].
• The MIEWS portal (Market Intelligence and Early Warning System) tracks TOP prices and sends alerts so the government can step in [7].

7. Types of inflation by pace

Type	Pace	Effect
Creeping	Slow and steady, below about 3% a year	Generally harmless. It can even encourage firms to invest
Galloping	Double- or triple-digit rates a year (10%–999%)	People lose trust in money and move savings into gold and land
Hyperinflation	Over 50% a month (usual definition)	The currency is destroyed. People turn to barter or foreign currency

• How big is 50% a month? 1.5¹² ≈ 130. Prices rise about 130 times in one year, which is roughly 12,900% a year.
• Examples of hyperinflation: Germany (Weimar Republic) 1923, Zimbabwe 2008, Venezuela (late 2010s).
• Common cause: the government prints money to pay for large deficits while output falls.

8. Vocabulary of direction

Term	Meaning	Numerical illustration
Disinflation	Inflation slows down. Prices still rise, but more slowly	6% → 4%; index 100 → 106 → about 110.2
Deflation	The general price level falls; inflation is negative	Index 100 → 98 = −2%
Reflation	Deliberate policy to push inflation and output back to normal after deflation or very low inflation	Rate cuts plus more government spending

• Trap: falling inflation is not falling prices. 6% → 4% is disinflation. Only a negative rate is deflation.
• Why deflation is harmful:
• Real burden of debt goes up. A borrower owes a fixed ₹1 lakh. If prices fall 5%, the loan now costs about 5.3% more in real goods (1/0.95).

• People postpone spending, expecting lower prices later → demand falls → firms cut output and jobs → prices fall further. This is a deflationary spiral.

• Reflation is used when deflation is a risk. Tools include lower interest rates, more liquidity and higher government spending.

9. Special terms

• Skewflation: prices of a narrow group (pulses, onions, food) rise sharply while overall inflation stays moderate.

• Headline CPI hides the pain, because poor households spend a larger share on these items.

• Protein inflation: prices of protein-rich foods (pulses, milk, eggs, meat, fish) rise.

• Cause: as incomes rise, people add more protein to their diet. Demand grows faster than supply. So this is a structural cause, not a seasonal one.

• Shrinkflation: the pack gets smaller while the price stays the same (e.g. a ₹10 biscuit pack goes from 100 g to 90 g).

• The price per gram actually rose by about 11% (100/90).
• A hidden price rise like this is missed unless index makers adjust for quantity, which means comparing price per unit, not price per pack.

Prelims Hooks

• Y-o-y CPI inflation formula (MoSPI): (Iₜ − Iₜ₋₁₂)/Iₜ₋₁₂ × 100. NCERT's weekly WPI formula is outdated; WPI is now monthly.
• Disinflation ≠ deflation: inflation falling from 6% to 4% is disinflation. Only a fall in the price level itself is deflation.
• Base effect: a high base (last year's spike) lowers this year's y-o-y rate even when prices are rising. A low base raises it.
• RBI's split: momentum = m-o-m change this month. Base effect = m-o-m change in the same month last year.
• New CPI base 2024 = 100, first released 12 February 2026. Weights come from HCES 2023-24. It follows COICOP 2018 and has 358 weighted items (up from 299).
• Food and Beverages weight (Combined): 45.86% (CPI 2012) → 36.75% (CPI 2024, COICOP structure).
• CPI 2024 index formulas: Jevons index at the elementary level. Young/Modified Laspeyres at higher levels.
• Inflation target: 4% CPI, band 2–6%. It is set by the Central Government in consultation with RBI under Section 45ZA, RBI Act, every five years. First notified on 5 August 2016.
• Hyperinflation is conventionally more than 50% per month. Creeping inflation is below about 3% per year.
• Operation Greens (TOP): announced in Budget 2018-19 with ₹500 crore and run by MoFPI. It is not run by the Agriculture Ministry, which makes this a common trap.

Mains Points

• Reading headline inflation carefully: a sharp fall in y-o-y CPI can come mostly from a favourable base effect. In that case price momentum is still positive. RBI's momentum and base-effect split, as used in 2021 and 2024, stops policy from cutting rates too early or raising them too late. This matters for credibility under the 4% (±2%) target.
• Food-heavy CPI and monetary policy: food shocks come from the monsoon, heatwaves and TOP perishability. These are supply shocks that the repo rate cannot fix. The drop in the food weight from 45.86% to 36.75% (CPI 2024) makes headline CPI a better guide to demand-side pressure. Supply-side tools are still needed: Operation Greens, storage, cold chains and MIEWS alerts.
• Distribution and hidden inflation: skewflation and protein inflation hurt poor and rural households more, because food takes a larger share of their budget. Shrinkflation understates true price rises. Regular base revisions (every 3–5 years), online price collection and quantity adjustment make the CPI more accurate. This affects wage indexation, DA and the real value of welfare benefits.
• Deflation risk and reflation: falling prices raise the real burden of debt and make people postpone spending. That is why inflation-targeting frameworks have a lower tolerance band (2%) and not just an upper one. Moderate, stable inflation is the goal, not zero inflation.