Marginal Propensity to Import (MPM) Calculator

When a country’s income rises by one dollar, how many cents of that dollar leak straight back out on imports? That share is the marginal propensity to import (MPM), and it decides how much of any stimulus, tax cut or export boom actually stays at home. This calculator divides the change in imports by the change in income, then shows the result as a decimal, a percentage and a per-dollar figure, with a plain-English verdict on whether import sensitivity is low, moderate or high.

Quick Answer

How to use the MPM calculator

Enter the change in imports and the change in income for the same period, then click Calculate. The tool divides the first by the second and reports the decimal, the percentage, the per-dollar leakage and a verdict band.

1. Work out the change in imports first. Subtract the earlier period's imports from the later period's. Both of these inputs are changes over time, not totals; if you are still holding two raw readings, a marginal change calculator turns a pair of levels into the change you need.
2. Use the matching change in income. Same start date, same end date. Income here means whichever aggregate your model runs on: national income, disposable income or GDP. If your two income readings are GDP figures a year apart, the GDP growth rate calculator confirms the size of the move you are dividing into.
3. Keep the price basis consistent. Both inputs nominal or both real. Mixing a nominal imports change with a real income change bakes inflation into the ratio and calls it behaviour.
4. Read the verdict with the number. The same 0.30 means something different for a small island economy than for a continental one, but the band tells you where your figure sits against the usual 0 to 1 range.
5. Try the recession case. Enter both changes as negatives, for example imports down 30,000 and income down 200,000. The tool returns 0.1500, because a ratio of two falls is still positive. Most rival tools refuse negative inputs entirely.

The MPM formula and where it comes from

MPM = change in imports divided by change in income: MPM = ΔM / ΔY. It is the slope of the import function, the line economists write as M = M₀ + mY, where M₀ is the imports an economy buys even at zero extra income and m is the MPM itself.

That slope is why MPM shows up everywhere in open-economy macroeconomics. Net exports equal exports minus imports, so as income rises, net exports fall along a line with slope −MPM: each extra dollar of income drags the trade balance down by exactly the MPM in cents. The Bureau of Economic Analysis NIPA handbook sets out how the underlying income and trade aggregates are measured in the US national accounts, and the import function itself is standard Keynesian apparatus: imports are induced spending, driven by income rather than fixed.

One honest limit: a two-point MPM is an average slope between two periods, not a laboratory measurement. Economists estimating MPM seriously run regressions on long runs of quarterly data, because a single quarter mixes the income effect with exchange-rate moves, tariff changes and one-off stockpiling. The two-point figure is the right starting point for coursework, policy sketches and sanity checks, and it is what every calculator on this keyword computes.

Worked example: five runs through the tool

Each row below is a real run of the calculator above, so you can reproduce every figure exactly. The pre-filled run is the first row: imports up 250,000 on income up 2,000,000.

Read the band edges carefully, because the tool draws its lines in specific places: exactly 0.2000 and exactly 0.5000 both land in Moderate. The verdict flips to High only above 0.50, and a result below zero gets its own message, because imports moving against income usually means something else in the data changed at the same time, such as a currency crash making imports dearer while incomes rose.

What counts as a low, moderate or high MPM

The calculator sorts every result into one of four readings. The bands are this page's stated convention, printed here so the verdict never surprises you:

Whole-economy estimates usually sit between 0 and 1, and where a country lands depends on how much it can make at home. Economies with deep domestic manufacturing and services tend to run lower MPMs; small or import-dependent economies, where food, fuel and machinery mostly come from abroad, run higher ones. The World Bank's imports of goods and services series shows the level of import dependence by country, which is the backdrop the marginal figure moves against.

MPM and the open-economy multiplier

MPM matters most because it shrinks the multiplier. In the withdrawals form of the Keynesian model, the multiplier is 1 / MPW, and total withdrawals per extra dollar are MPW = MPS + MPT + MPM: the shares that leak into saving, taxes and imports.

Put numbers on it. Suppose MPS is 0.10, MPT is 0.20 and MPM is this page's worked example, 0.125. Then MPW = 0.425 and the multiplier is 1 / 0.425, about 2.35: a dollar of government spending becomes roughly $2.35 of income. Delete the import leakage (MPM of 0) and MPW falls to 0.30, so the multiplier rises to about 3.33. That gap, nearly a whole dollar of effect per dollar spent, is the entire policy argument for knowing your MPM before designing a stimulus. To see what a given multiplier does to jobs specifically, run the same logic through the employment multiplier calculator.

MPM is also one of the marginal propensities that must sum consistently: MPC + MPW = 1, because every extra dollar is either consumed or withdrawn. If your MPM estimate makes the family of propensities sum to more than 1, one of the estimates is wrong, and MPM is a good place to re-check, since two-point trade figures are noisy.

MPM next to MPC, MPS and MPT

The four marginal propensities answer four different "where does the next dollar go?" questions. MPM is the only one that leaves the country:

A common student error is treating MPM as a slice of MPC. It is related but distinct: consumption spending includes imported goods, so part of MPC leaks through MPM, yet the two are estimated from different data (consumption surveys versus trade statistics) and answer to different policies (tax and transfer design versus trade and exchange-rate policy).

What competing calculators miss

The MPM keyword is thinly served, and the gaps are consistent: bare ratios, no recession handling, and in one case arithmetic that does not survive checking.

• SavvyCalculator: a solid worked example and a percentage view, but it goes further and predicts total imports by multiplying MPM by current income. That treats imports as if they would be zero without income, ignoring autonomous imports entirely, so the forecast flatters the method. This page reports the ratio and its meaning, and does not invent a forecast the inputs cannot support.
• Calculator Ultra: clean formula page with a $500 / $2,000 example, but no interpretation bands, no per-dollar figure and no stated handling of falling income or falling imports. A student in a recession year gets a number with no guidance on whether it is usable.
• Wall Street Oasis: a respected glossary with no calculator at all, and one of its printed examples divides 500 by 1,500 and reports 0.30; the correct figure is 0.33. Small slip, but it is exactly the kind of thing a worked example exists to prevent.
• The gap this page fills: decimal, percentage and per-dollar outputs together, a stated verdict band with its edges printed, negative changes accepted and explained, the multiplier connection worked with real numbers, and a step-by-step breakdown under every result.

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