Investment multiplier

Also called: Autonomous expenditure multiplier, multiplier · Topic: Aggregate Demand, Income Determination and the Multiplier · NCERT: Class 12, Ch 4 "Determination of Income and Employment"

Meaning

The investment multiplier (k) is the ratio of the rise in equilibrium output (national income) to the first rise in autonomous spending (spending that does not depend on income, such as planned investment) that caused it:

k = ΔY/ΔĀ = 1/(1 − MPC) = 1/MPS

It matters because it shows that ₹1 of new spending can raise national income by more than ₹1. This is the core of the Keynesian case for using government spending to fight a slump. Keynes used the idea in the 1930s to work out how much government spending was needed to reach full employment when private investment was too low [5].

Explanation

Basic terms

• Autonomous spending (Ā): spending that does not depend on income. In the simple model, Ā = C̄ (autonomous consumption) + Ī (planned investment).
• MPC (c): the share of each extra rupee of income that people spend. c = ΔC/ΔY, and 0 ≤ c ≤ 1.
• MPS (s): the share of each extra rupee of income that people save. s = 1 − c.
• Equilibrium output (Y*): the output at which aggregate demand (total planned spending, AD = Ā + cY) equals output.
• Solving Y = Ā + cY gives Y* = Ā/(1 − c).
• So any change in Ā is multiplied by 1/(1 − c).

How it works: the round-by-round mechanism (NCERT Table 4.1)

• The shock: C = 40 + 0.8Y. Investment rises from 10 to 20.
• Before: Ā = 50, so Y* = 50/0.2 = 250.
• After: Ā = 60, so Y* = 60/0.2 = 300.

• ΔY = 50 from ΔĪ = 10, so k = 5.

• Round 1: output becomes income.

• Firms produce 10 more to meet the new investment demand.

• This 10 is paid out as wages, rent, interest and profit, so household income rises by 10.

• Round 2: income becomes spending.

• Households spend 0.8 × 10 = 8. Firms produce 8 more, and that 8 becomes someone's income.

• Later rounds get smaller.

• The next rounds add 6.4, then 5.12, then 4.096, and so on.

• Each round shrinks because 0.2 of it is saved. Saving is a leakage (income that does not come back as demand).

• Adding up the rounds (a geometric series):

• ΔY = 10 × (1 + 0.8 + 0.8² + …) = 10 × 1/(1 − 0.8) = 50.

• After 4 rounds, income has risen by only 29.52. The other 20.48 comes from all the later, smaller rounds.

• When it stops: new saving = 0.2 × 50 = 10, which equals the first rise in investment. Planned saving again equals planned investment.

• Another example: investment rises by $1 million and MPC = 0.6. Round 2 adds $600,000 of income [5]. k = 1/(1 − 0.6) = 2.5, so income rises by $2.5 million.

On the graph

• AD shifts up in parallel by ΔĀ = 10. Only the intercept changes. The slope (c = 0.8) stays the same.
• Excess demand appears at the old output.
• At the old output, demand is higher than output. The gap E₁F is the excess demand.
• Firms' stocks run down, so firms produce more.

• Output keeps rising until the new AD line meets the 45° line at E₂.

• What the graph compares: the rise in output (E₁G = 50) is larger than the rise in autonomous spending (E₁F = 10). The difference is the multiplier at work.

• Parametric shift (a line moves because one of its fixed numbers changes):
• A change in Ā shifts AD in parallel.
• A change in c swings AD. A higher c makes AD steeper.
• Example: Ā = 50. If c rises from 0.8 to 0.9, Y* rises from 250 to 500, and k rises from 5 to 10.

What makes it rise or fall

MPC	MPS	Multiplier
0.9	0.1	10
0.8	0.2	5
0.75	0.25	4
0.5	0.5	2
0	1	1 (limit)
1	0	∞ (limit)

• Higher MPC → bigger multiplier. Less leaks out as saving each round, so more rounds of income are created.
• Limits: in the simple closed economy, k lies between 1 and ∞. It can never be below 1.
• c = 0: only the first 10 is added, so k = 1.

• c = 1: the rounds never shrink, so k = ∞. This is only a theoretical limit.

• More leakages → smaller multiplier.

• Imports: open-economy k = 1/(1 − c + m), where m is the marginal propensity to import (the share of each extra rupee spent on foreign goods). With c = 0.8 and m = 0.3, k = 2, compared with 5 in a closed economy.

• Proportional tax (t): k = 1/(1 − c(1 − t)). With c = 0.8 and t = 0.25, k = 2.5.

• It works in reverse.

• Investment falls by 10 → income falls by 10 → consumption falls by 8 → income falls again.

• Output falls by 50 in total. This is how a slump (a sharp fall in business activity) spreads through the economy, as in the Great Depression behind Keynes's work.

• NCERT misprint: equation 4.5 prints "1/S". It should be 1/s, where s is the MPS (a ratio), not S, the amount of saving in rupees.

In India

• Policy link: the multiplier connects a change in spending to the change in national income that follows. This link is a key part of the Keynesian argument that fiscal policy works in a predictable way [5].
• What kind of spending matters, not just how much (RBI Bulletin, June 2021) [2]:
• Capital outlay (spending that creates assets, such as roads and power plants) raises growth more than revenue expenditure (day-to-day spending such as salaries, interest and subsidies) [2].
• Revenue spending is most of what the Centre and the States spend. So the impact multiplier (the first-year effect) of total government spending is less than one [2].

• Before COVID-19, the government supported demand through heavy revenue spending for 6–7 quarters. The recovery still did not last. The study linked this to the low, short-lived multipliers of revenue spending [2].

• Capex multiplier: studies cited by the government (Union Budget 2024-25) estimate that public spending on infrastructure raises GDP by about 2.5 to 3.5 times the amount spent over the medium term [4].

• Policy response (Economic Survey 2025-26) [3]:
• The Centre's capital outlay rose by about 89%, from ₹5.92 lakh crore (FY22) to ₹11.21 lakh crore (FY26 BE). The stated reason is the strong multiplier effect of infrastructure [3].

• The Centre gives States 50-year interest-free loans for capital spending under the Special Assistance to States for Capital Investment. The stated reasons are its higher multiplier and crowding in (drawing in more private investment) [3].

• Indian limit: V.K.R.V. Rao (1952). In an underdeveloped economy the real multiplier (the rise in actual output, not money income) is weak, for three reasons:

• Supply bottlenecks: infrastructure, power and capital are short, so extra demand cannot quickly become extra output.
• Large non-monetised sector: much output is used by the family that grows it (for example, a farm family eating its own grain), so spending does not pass easily from one market round to the next.
• Inelastic farm output: extra income is mostly spent on food, but farm supply cannot rise within a season.
• Result: extra demand raises prices rather than output.

Don't confuse with

• Accelerator: the multiplier says a change in investment causes a larger change in income. The accelerator says a change in income or output causes a change in investment. The direction of cause and effect is reversed.
• Money multiplier: this is about banks creating credit from reserves, and it depends on the reserve ratio. The investment multiplier is about income created through spending rounds, and it depends on the MPC.
• Open-economy multiplier: 1/(1 − c + m) is smaller than the closed-economy 1/(1 − c) because imports are an extra leakage (2 against 5 in the NCERT example).
• Impact multiplier: this is only the first-year effect of spending. For total government spending in India it is below 1 (RBI, June 2021) [2]. The textbook multiplier is the full effect after all rounds, and in the simple model it is never below 1.

Prelims Hooks

• k = ΔY/ΔĀ = 1/(1 − MPC) = 1/MPS. With MPC = 0.8, k = 5, so ₹10 of extra investment raises equilibrium income by ₹50.
• In the simple closed-economy model, k lies between 1 (MPC = 0) and ∞ (MPC = 1). It can never be below 1.
• Trap: "a higher saving rate raises the multiplier" is wrong. A higher MPS gives a smaller multiplier.
• Leakages are saving, taxes and imports. Injections are investment, government spending and exports. Open-economy k = 1/(1 − c + m).
• A change in investment shifts AD in parallel. A change in MPC swings AD. Both are parametric shifts. The multiplier also works in reverse, making slumps bigger.
• RBI (June 2021): capital outlay has higher growth multipliers than revenue expenditure. V.K.R.V. Rao (1952): the multiplier is weak in underdeveloped economies, so extra demand raises prices rather than output [2].

Mains Points

• Quality of spending over quantity (GS-III, fiscal policy):
• Revenue spending has low, short-lived multipliers. Capex has higher ones, about 2.5–3.5 over the medium term [2][4].
• This supports India's capex push: ₹5.92 lakh crore (FY22) to ₹11.21 lakh crore (FY26 BE), plus 50-year interest-free capex loans to States [3].

• Trade-off: counter-cyclical spending (spending more when the economy slows) raises the fiscal deficit and debt, so debt sustainability limits how far it can go.

• Keynes versus Indian conditions:

• Rao's 1952 point still applies. Where supply bottlenecks, informality and slow farm supply exist, pure demand stimulus turns into inflation.

• So stimulus should come with supply-side reforms: infrastructure, farm productivity and formalisation. Capex helps because it adds both demand and capacity [2][3].

• Import leakage and self-reliance:

• A high marginal propensity to import, for example on electronics and energy, cuts the domestic multiplier (from 5 to 2 in the NCERT example).
• This gives a macro argument for Make in India and PLI, which aim to keep more of each spending round at home.

Related concepts

• Multiplier mechanism
• Parametric shift
• Open economy multiplier

Read more

• The investment multiplier and its round-by-round mechanism