Let us start with the simplest case, following a household with €2,500 a month. DISPOSABLE INCOME is everything it takes in — wages, pensions, benefits, rents received — minus taxes and social contributions. It has only two possible uses: consume, or not. If it consumes €2,050, its SAVING is what is left, S = R − C = €450. Divide that residual by income and you get the saving RATE: 450/2,500 = 18%. Note carefully what the object is: it is not a sum somebody wanted to set aside, it is a subtraction recorded after the fact. Hence a property we shall use everywhere: since S and C share out the whole of R, the saving rate and the consumed share add up to 100% — here 18% and 82%.

Let us go from the household to the country, and this is where almost everybody trips. Take the two households of the poll again. The first earns €1,500 and saves 0%: its saving is nil. The second earns €4,500 and saves 30%: €1,350. Average the two RATES and you get (0 + 30)/2 = 15%. But that is not how a country is measured: you add up the saving (€1,350), you add up the income (€6,000), and you divide — 22.5%. Why the gap? Because in a ratio of aggregates, each household weighs **in proportion to its income**, not one vote each. The rich one counts three times more here. Formally, the national rate is an average of individual rates WEIGHTED by incomes. So what the algebra proves is precise: as soon as incomes AND rates differ, the aggregate departs from the simple average of rates — and it departs UPWARDS when it is high incomes that save the most. Whether that is actually the case, no algebra can say: it has to be measured. And the measurement is striking. According to the 2022 national accounts, the net saving rate of the poorest 20% of households is **−29%** — they dissave — that of households near the median **+6%**, and that of the richest 20% **+27%**. So the middle household saves around 6%, while the country posts nearly 18%. Keep the right words: “the French save 18%” describes a NATION, never a French person.

Back to our household and its €450. Where do they go? Suppose it repays €250 of principal on its mortgage and invests €200. Both are USES of saving, because in both cases its net wealth rises: repaying principal wipes out a debt. Buying housing follows the same logic — national accountants say that saving FINANCES that purchase rather than IS it, but the practical consequence is identical: those euros end up in no account. So two rates are measured, never to be confused: the TOTAL rate (450/2,500 = 18%) and the FINANCIAL saving rate, which counts only investments (200/2,500 = 8%). France showed a contrast of the same order at the end of 2025: 17.9% and 8.6% (our household is not France; its figures were merely chosen to resemble it). In other words, more than half of what the French save goes into bricks and mortar. (The interest on the loan is neither saving nor consumption: it is deducted upstream from disposable income.)

Here is the most counter-intuitive result of the subject, and it takes three lines to prove. Let us take a whole country, over one year, with investment I set by firms. Three simplifications, to be stated at once since they are what makes the result so clean: no state (no public spending, no taxes), no trade with abroad, and idle production capacity — in other words an economy running below par, where demand is what limits activity. Then everything produced is either consumed or invested: Y = C + I. And households consume a share (1 − s) of their income: C = (1 − s)·Y, where s is the saving rate written as a decimal — 0.20 for 20%. Mind the notation, the two letters live side by side: capital S is saving in euros, lower-case s is the rate. Now substitute C into the first equality: Y = (1 − s)·Y + I. Bring the Y terms to the same side: Y − (1 − s)·Y = I. But Y − (1 − s)·Y = Y·[1 − (1 − s)] = Y·s. What is left is s·Y = I, that is, **Y = I / s**. That writing should ring a bell: 1/s is exactly the Keynesian multiplier, since s = 1 − c where c is the consumed share (course “The fiscal multiplier”). The country's income is investment multiplied by 1/s — and it is precisely because that multiplier shrinks when s rises that what follows surprises. Now compute saving: S = s·Y = s × I/s = **I**. Total saving equals investment, WHATEVER the saving rate. Put figures on it to believe it: with I = 200 and s = 20%, income settles at 1,000 and saving at 200. If all households decide to save 25%, income falls to 800 — and saving is still 200. They have saved a bigger share of a smaller cake, for exactly the same amount. This is Keynes's PARADOX OF THRIFT: wanting to save more, all together, does not make more saving appear — it makes income disappear. Click each term: