Inflation and Purchasing Power

Learning goals

You will distinguish a price level from an inflation rate, calculate year-on-year changes and real purchasing power, and connect demand and supply pressures to suitable policy responses.

A basket rather than one price

Inflation is a rise in the general price level over time. A single vegetable becoming expensive does not by itself prove broad inflation. CPI tracks consumer prices for a defined basket, with weights reflecting spending importance. Its movement need not match your personal bill. Food, transport, rent and services have different shares across families. A price index is unit-free; 150 is not ₹150.

Inflation disinflation and deflation

If prices rise 8% and then 4%, inflation has slowed but the price level still rises. This is disinflation. Deflation means a falling general price level, or negative inflation. A lower inflation rate can partly reflect a high comparison base; inspect index levels before declaring that all prices have fallen. Compare the same month in successive years for year-on-year inflation.

Causes and distribution

Demand can rise faster than available output. Supply shocks can raise costs or reduce availability. The same price rise may hurt a food-buying labourer but benefit a farmer only if saleable output and realised prices compensate for input costs. Unexpected inflation can reduce the real value of fixed nominal debt, but debt terms and income changes matter. There is no universal winner or loser.

Formulas

Inflation (%) = [(index now ÷ comparable earlier index) − 1] × 100. Year-on-year uses the same month one year earlier; month-on-month uses the previous month. Name the comparison.

Teaching fixed-basket index = [Σ(current price × base quantity) ÷ Σ(base price × base quantity)] × 100. This is a simplified model; actual CPI compilation has detailed aggregation and quality procedures.

Real income in base-period purchasing power = nominal income × 100 ÷ price index. Purchasing-power index of one rupee = 10,000 ÷ price index, with the base set to 100.

Exact real income growth (%) = {[(1 + nominal income growth) ÷ (1 + inflation)] − 1} × 100. Enter growth rates as decimals. Nominal growth minus inflation is only an approximation.

Rajasthan application

Rajasthan application: a rainfall shock can reduce crop supply and raise food or fodder costs; fuel costs can affect long-distance freight. Analyse exposure before prescribing a remedy. Supply measures include logistics and storage improvements; targeted support can protect vulnerable buyers. Monetary tightening works through demand and credit with lags and cannot directly create rainfall. Do not present current inflation targets or state rates without checking an official dated release.

Worked example 1 Calculate the rate

The CPI is 150 this June and 144 last June. Find year-on-year inflation.

Change = 6 index points. Inflation = (6/144) × 100 = 4.1667%, about 4.17%. Six index points are not 6% inflation.

Worked example 2 Household basket

A fixed basket has 10 kg grain and 2 litres oil. Base prices are ₹30/kg and ₹100/litre; new prices are ₹33/kg and ₹110/litre. Find basket inflation.

Base cost = 10×30 + 2×100 = ₹500. New cost = 10×33 + 2×110 = ₹550. Index = 110; inflation = 10%. Keep quantities fixed to measure price change.

Worked example 3 Salary and real gain

Monthly pay rises from ₹20,000 to ₹22,000 while the relevant price index rises from 100 to 108. Find the real gain.

New real pay = 22,000 × 100/108 = ₹20,370.37 in base purchasing power. Real growth = (1.10/1.08 − 1) × 100 = 1.85%, not exactly 2%.

Exercise 1

The index goes 100 → 110 → 115.5. What is second-period inflation?

(115.5/110 − 1) × 100 = 5%. Disinflation from 10% to 5%; prices have not fallen.

Exercise 2

An index falls from 125 to 120. Inflation or deflation?

(120/125 − 1) × 100 = −4%. This is deflation for that index and interval; it need not describe every item.

Exercise 3

Nominal income is unchanged and prices rise 25%. How much purchasing power is lost?

1/1.25 = 0.80: a 20% loss, not 25%. The denominator changes when converting price growth into purchasing-power loss.

Exercise 4

In a two-group model food has weight 60% and rises 10%; other items have weight 40% and rise 5%. Find weighted inflation.

0.60×10 + 0.40×5 = 8%. This result assumes fixed base expenditure weights and comparable group indices. A simple unweighted mean of 7.5% is wrong here.

Common errors

A falling positive inflation rate is not falling prices. Do not subtract index numbers and call the result a percentage. Do not replace CPI with the GDP deflator: their coverage and weighting differ. Do not treat the headline average as every household’s experience. Avoid using old base-year weights as current facts.

5 marks, about 50 words: Distinguish disinflation from deflation with a numerical illustration.

Model answer: Disinflation means slower price increases: an index moving from 100 to 110 and then 115.5 has inflation of 10% followed by 5%. Prices still rise. Deflation means a price-level fall, such as an index declining from 125 to 120, yielding −4% inflation. Always specify the period and index.

Rubric 5: both definitions 2; calculations 2; price-level conclusion 1.

10 marks, about 150 words: Explain why a food-price shock affects Rajasthan households differently and suggest a balanced policy response.

Answer plan: separate net buyers from net sellers; examine food expenditure share, wages, farm yields and input costs; identify drought/logistics as possible channels, not claimed current events; protect vulnerable households through targeted support and improve supply; explain monetary-policy limits for a local supply shock and risk of broad demand stimulus; conclude with evidence on prices, availability and household exposure.

Rubric 10: distribution 3; causal mechanism 2; balanced policies 3; Rajasthan context and conclusion 2.

Sources and scope / स्रोत और सीमा

Checked 30 September 2026. Original explanations, fictional numerical data, practice and teaching rubrics; not official questions or an official answer key. RPSC syllabus alignment is selective, not complete coverage. / जाँच 30 सितंबर 2026। व्याख्याएँ, काल्पनिक आँकड़े, प्रश्न और शिक्षण मानदंड मौलिक हैं; आधिकारिक प्रश्न या उत्तर-कुंजी नहीं। चयनित पाठ्यक्रम अंश, संपूर्ण कवरेज नहीं।

RPSC RAS Mains Scheme and Syllabus 09 January 2026 (https://rpsc.rajasthan.gov.in/Static/Syllabus/238A2E0E-B0D0-49C2-8E5E-D299A915037F.pdf) — Paper I Unit II economics, p3; foundation alignment only

MoSPI FAQs (https://mospi.gov.in/faq) — Current versus constant prices; implicit deflator; CPI interpretation; do not splice different series

MoSPI Manual on Consumer Price Index Chapter III (https://mospi.gov.in/sites/default/files/publication_reports/manual_cpi_2010.pdf) — Durable index concepts, not current basket weights or base year

RBI Financial Awareness FAQs (https://m.rbi.org.in/commonman/english/scripts/FAQs.aspx?Id=711) — Inflation and purchasing power

Analogy

Imagine a monthly shopping basket as a measuring ruler. Repricing the same basket reveals how much more money is needed. Limitation: families substitute goods, quality changes and new products appear. CPI is an average indicator, not a perfect cost-of-living measure for every household.

Quick reference

Price level describes prices at a given time; inflation is its rate of change over an interval. Compare like periods. Fix basket quantities in elementary index calculations. Deflate money income for purchasing power. Demand and supply causes require different, sometimes complementary, remedies.