What it means
Marginal productivity is the extra output created by adding one more unit of an input, such as one more employee or one more machine hour. The law says that after a certain point, that extra output starts to shrink as more of the input is added to a fixed amount of everything else.
Total output usually keeps rising, but at a slower and slower rate. The reason is simple.
Fixed inputs such as floor space, equipment and management time have to be shared among a growing number of workers. Early hires fill obvious gaps and specialise in tasks, while later hires queue for the same machines or get in each other's way.
For a finance professional, this law is the bridge between operations and cost. When extra workers produce less and less, the cost of each additional unit of output rises because the wage bill rises at a steady pace while output rises more slowly.
That is why marginal cost curves usually bend upwards. Managers use the idea to decide how many people to hire, how many shifts to run and when to invest in more capacity instead.
If an additional worker costs more than the value of the extra output they add, hiring them destroys profit. The sensible stopping point is where the value of the marginal product equals the marginal cost of the input.
An important nuance is the time frame. The law applies in the short run, when at least one input such as factory size cannot be changed.
In the long run the firm can expand everything together, so the issue becomes economies and diseconomies of scale instead.
In practice
Real-world examples.
Example
A call centre keeps its 20 phone lines and 20 desks but adds a seventh and an eighth shift of agents on the same equipment. Each extra agent has to wait for a free headset and desk, so calls handled per hour grow by less with every addition. The operations manager stops adding agents when the extra calls no longer cover the extra wages.
Example
A farm with a fixed 50 acres hires more seasonal pickers at harvest. The first few pickers clear rows quickly, but by the time the twelfth arrives the pickers are crowding the same rows. The farm owner compares the extra crates picked per day to the daily wage before agreeing to more hires.
Example
A software team of four developers works on one code base and adds six more people mid-project. Coordination meetings and merge conflicts multiply, and the team ships fewer new features per person than before. The product director concludes that the extra headcount is adding less than it costs.
Formula
Calculation
Marginal product of labour = change in total output / change in number of workers
A small bakery pays each worker $120 a day and sells each loaf for $10. With 1 worker it bakes 30 loaves, with 2 workers 70 loaves, with 3 workers 100 loaves, with 4 workers 120 loaves and with 5 workers 130 loaves. The marginal products are 30, then 70 - 30 = 40, then 100 - 70 = 30, then 120 - 100 = 20, then 130 - 120 = 10 loaves. The fifth worker adds 10 loaves worth 10 x $10 = $100 but costs $120, so hiring that worker loses $20 a day, while the fourth worker adds 20 x $10 = $200 against $120 of cost and is worth hiring.Case study
Seen in the real world.
Harbour Crate Logistics is an illustrative, fictional warehouse operator that handled a surge in online orders by adding pickers to its single packing hall. For the first three extra pickers, daily parcels shipped rose by about 400 each, which easily justified a daily cost of $150 per person.
By the ninth extra picker, aisles were congested and each new person added only about 60 parcels a day, worth roughly $120 in handling fees against a $150 wage. The finance manager showed the operations team that the last few hires were losing money, and the company chose instead to lease a second packing hall. The illustrative point is that once a fixed input is the bottleneck, the next dollar is better spent on that input than on more labour.
Watch out
Common mistakes.
- Believing that diminishing marginal productivity means total output falls, when output normally keeps rising and only the extra gain shrinks.
- Applying the law to a long-run decision where all inputs can be expanded together, which is a question about scale rather than diminishing productivity.
- Ignoring the early stage where adding workers raises marginal productivity through specialisation, and assuming returns diminish from the very first hire.
Questions
People also ask.
Is this the same as diseconomies of scale?
No. Diminishing marginal productivity is a short-run effect of adding one input to fixed others, while diseconomies of scale describe rising average costs when the whole business grows too large.
Can marginal productivity turn negative?
Yes, if a workplace becomes so crowded that an extra worker actually reduces total output, though sensible managers stop hiring well before that point.
How does this affect pricing decisions?
Because extra output costs more to produce at high volumes, a firm running near capacity may need a higher price to make additional sales worthwhile.
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