What Is the Law of Diminishing Marginal Returns? Key Concepts and Examples
By Markets & Investing DeskUpdated Nov 10, 2026
Definition
The law of diminishing returns says that adding more of one input while other inputs stay fixed eventually makes each extra unit add less output, even as total output rises.
Key takeaways
- Marginal product equals the change in total output divided by the change in the variable input, or MP = ΔQ / ΔL.
- In the bakery example, diminishing returns start with the third worker though total loaves keep rising until the fifth.
- Marginal cost equals the wage divided by marginal product, so a $150 worker adding 5 loaves costs $30 per extra loaf.
- Returns to scale differ because they are long run and change all inputs in the same proportion.
The law of diminishing returns (formally, the law of diminishing marginal returns) states that when a producer keeps adding units of one input while holding every other input fixed, the extra output from each additional unit eventually gets smaller. Total output can keep rising for a while. What shrinks is the marginal gain, the output added by the last unit of input.
The principle is also called the principle of diminishing marginal productivity and the law of variable proportions. It is a short-run idea: it applies only while at least one factor, such as land, equipment or floor space, cannot change.
How diminishing marginal returns work
Production combines factors of production such as land, labor and capital. When one factor is fixed, each new unit of the variable factor has a smaller share of the fixed factor to work with.
Calculating marginal returns
The key measure is marginal product (MP), the change in total output (Q) from one more unit of the variable input (L):
MP = ΔQ / ΔL
Average product (AP) is total output divided by total units of the input: AP = Q / L. Diminishing marginal returns begin at the point where MP starts to decline, often called the point of diminishing returns.
Worked example: a bakery with one oven
Hypothetical example. A bakery has one oven and a fixed shop. It hires workers one at a time, and daily output changes as follows:
| Workers | Total loaves (Q) | Marginal product | Average product |
|---|---|---|---|
| 1 | 20 | 20 | 20.0 |
| 2 | 50 | 30 | 25.0 |
| 3 | 75 | 25 | 25.0 |
| 4 | 90 | 15 | 22.5 |
| 5 | 95 | 5 | 19.0 |
| 6 | 92 | −3 | 15.3 |
The figures show the three stages economists describe:
- Increasing marginal returns (workers 1 to 2): the second worker adds more than the first because the two can specialize, one mixing and one baking.
- Diminishing marginal returns (workers 3 to 5): each worker still raises total output, but by less than the one before. The third adds 25 loaves, the fourth 15, the fifth 5.
- Negative returns (worker 6): the shop is so crowded that total output falls by 3 loaves.
Diminishing returns set in at the third worker even though total output keeps climbing until the fifth. Confusing “smaller gains” with “losses” is the most common misreading of the law.
Interpreting the result: the link to cost and supply
Assume each worker costs $150 per day and nothing else changes. The marginal cost of a loaf is the wage divided by the marginal product:
- Third worker: $150 / 25 = $6 per extra loaf
- Fourth worker: $150 / 15 = $10 per extra loaf
- Fifth worker: $150 / 5 = $30 per extra loaf
As marginal product falls, each additional loaf costs more to produce. A profit-seeking firm will only expand output if the selling price covers that rising marginal cost, so it supplies more only at higher prices. This is the mechanism behind the upward-sloping short-run supply curve.
Why the law matters
In practice the law guides several decisions:
- Hiring and staffing: a manager compares the value of a worker’s marginal product with the wage. Once the extra output is worth less than the extra cost, adding staff loses money even if total output still rises.
- Capital investment: adding machines to a fixed workforce shows the same pattern, so growth models built on diminishing marginal returns to capital predict that adding capital alone contributes less and less to GDP growth.
- Resource allocation: every unit put into a low-return use could go elsewhere, so falling marginal returns raise the opportunity cost of continuing.
History
The French economist Anne-Robert-Jacques Turgot is credited with the first recorded statement of diminishing returns in the mid-1700s. James Anderson, Thomas Robert Malthus, David Ricardo and Johann Heinrich von Thünen developed it further.
Classical economists focused on agriculture. Ricardo called the idea the “intensive margin of cultivation”: adding labor and capital to a fixed plot of land yields successively smaller increases in harvest. Malthus used diminishing returns to argue that population grows geometrically while food production grows only arithmetically, so population would tend to outrun its food supply.
The two schools explain the cause differently. Classical economists attributed falling returns to declining input quality, such as farming poorer land as cultivation expanded. Neoclassical economists assume each unit of labor is identical and trace the decline to the strain extra units put on the whole production process when capital is fixed.
Diminishing returns vs. returns to scale
Diminishing marginal returns are a short-run effect: one input rises while at least one other stays fixed.
Returns to scale are a long-run concept: all inputs change in the same proportion.
- Decreasing returns to scale: doubling every input raises output by less than double, for example 60%.
- Constant returns to scale: doubling every input exactly doubles output.
- Increasing returns to scale (economies of scale): output rises by a larger percentage than inputs, for example doubling inputs triples output.
A firm can face diminishing marginal returns to labor in one factory and still enjoy increasing returns to scale when it builds a second, larger plant.
Diminishing returns vs. diminishing marginal utility
The two ideas share a shape but describe different sides of the market. Diminishing marginal returns concern production: each extra input adds less output. Diminishing marginal utility concerns consumption: each extra unit of a good gives a consumer less satisfaction than the previous one. The first helps explain supply curves, the second helps explain downward-sloping demand.
Limitations
- Constant technology: a new oven design, software or training method shifts the whole production schedule, so the point of diminishing returns can move.
- No precise turning point: the law predicts that marginal returns will eventually fall, but the unit at which this happens depends on the specific process and must be measured.
- Uniform inputs assumed: real workers and machines differ in quality, which can blur the pattern in actual data.
The Bottom Line
Managers deciding on hiring, equipment or how to allocate resources can use the law to see when adding more of one input stops paying. The useful test is whether the value of the extra output covers its extra cost, since total output can still rise after expansion has become unprofitable. The exact turning point depends on the specific process and changes with technology, so it has to be measured.
