Labor Demand Curve vs Backward-Bending Labor Supply Curve
Labor Demand Curve and Backward-Bending Labor Supply Curve are two Labor Economics concepts in AP Economics that students often mix up. The labor demand curve shows how many workers a firm hires at each wage, and for a single firm it is simply its marginal revenue product curve. The backward-bending labor supply curve shows hours worked rising with wages at first, then falling once the income effect of higher wages outweighs the substitution effect. Here is how they compare side by side.
Labor demand is derived demand: a firm wants workers for the revenue their output brings in, not for their own sake. A profit maximizer keeps hiring while the marginal revenue product of the next worker exceeds the extra cost of employing them, and stops where MRP equals the wage. That makes the firm's labor demand curve identical to the downward sloping part of its MRP curve. It slopes down because of diminishing marginal returns, since each extra worker adds less output than the last. Demand comes from employers and shifts when the product's price, worker productivity, or the price of a related input changes, while a change in the wage alone only moves the firm along the curve.
A wage increase has two opposing effects on an individual's hours. The substitution effect makes leisure more costly (forgone wages), encouraging more work; the income effect makes the worker richer, encouraging more leisure. At low wages the substitution effect dominates and the curve slopes up, but at high wages the income effect can dominate, so further raises lead to fewer hours and the curve bends backward.
Labor Demand vs the Backward-Bending Supply Curve: The Two Sides of One Wage Diagram
| Labor Demand Curve | Backward-Bending Labor Supply Curve | |
|---|---|---|
| Whose decision it describes | A firm deciding how many workers to hire | A worker deciding how many hours of leisure to give up |
| What it is built from | Marginal revenue product, which falls as more workers are added | The pull between the substitution effect and the income effect of a raise |
| Shape | Downward sloping at every wage | Upward at low wages, then turning back to the left at high wages |
| What a wage rise does to quantity | Reduces the number of workers the firm wants | Raises hours first, then cuts them once the income effect takes over |
| Why the shape changes as you move along it | Diminishing marginal product means each extra worker adds less output | Higher pay buys the same living standard in fewer hours, so leisure gets bought |
| What shifts the whole curve | Product price, worker productivity, the price of machines that replace labor | Non-labor income, preferences, population, and tax rates on earnings |
| Where it ultimately comes from | Derived demand, since labor is wanted only for what it produces | The worker's own choice between money and time |
The firm's curve is a marginal revenue product schedule with a wage laid across it
A labor demand curve is not a separate object to memorise. It is the marginal revenue product schedule read from a different direction. Take an illustrative firm selling output at 10 dollars a unit. The first worker adds 6 units a day, the second 5, the third 4, the fourth 3 and the fifth 2, because equipment and space are fixed. Multiply through and marginal revenue product runs 60, 50, 40, 30 and 20 dollars a day. Now lay a daily wage of 35 dollars across that list. Workers one to three each bring in more than they cost, at 60, 50 and 40, while the fourth brings in 30 and would lose the firm 5 dollars a day. The firm hires three. Cut the wage to 25 and the fourth worker becomes worth hiring at 30 against 25, so employment rises to four. Two points on a demand curve, generated without ever drawing one. The downward slope comes entirely from the falling marginal product, not from any decision to pay people less, and the same schedule is worked through step by step at /calculate/marginal-revenue-product.
The supply curve bends back because a raise makes an hour of free time more valuable too
A higher wage does two opposing things to one person. It makes an hour of leisure more expensive, since giving up work now costs more, which pushes toward working longer. It also makes the person richer at any number of hours, and free time is something people buy more of as they get richer, which pushes toward working less. At low wages the first effect wins. At high wages the second one does. Take an illustrative worker who chooses 40 hours a week at 20 dollars an hour, earning 800 dollars. Raise the wage to 40 and she works 45 hours for 1,800. Raise it to 60 and she cuts back to 35 hours, taking home 2,100. Hours fell while pay kept climbing, which is the bend. Two warnings for the exam. The bend belongs to one person's supply curve, so it is drawn for an individual and not for an industry. Market supply to a single occupation almost always slopes up throughout, because a higher wage there pulls in workers from other occupations even when everyone already in it works fewer hours. You can drag both curves at /sandbox/factor-markets.
Frequently asked questions
Why is the labor demand curve downward sloping?
Because of diminishing marginal product: with capital fixed, each additional worker adds less output than the one before, so the revenue each new worker generates is smaller. A firm hires only while that revenue covers the wage, so a lower wage is needed before more workers are worth taking on.
Why does the labor supply curve bend backward?
Because past a high enough wage, the income effect of a raise outweighs the substitution effect, so the worker responds by taking more leisure rather than working more hours. The wage is high enough that the target standard of living can be reached in less time, and time becomes the scarcer thing.
Does a backward-bending supply curve mean higher wages reduce total hours worked?
Not for a labor market as a whole, because the backward bend describes one individual and market supply to any single occupation also includes workers arriving from other occupations. Only for a whole economy at very high wages would the bend show up in total hours, and even then it appears slowly, as changes in standard working weeks and retirement ages.
Live Factor Markets graph. Drag the curves, or open the full version.
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