The point at which it is no longer advantageous to buy in bulk is known as marginal what?
Marginal BENEFIT. Buying in bulk stops being advantageous at the point where the marginal benefit of one more unit falls below its marginal cost — the extra satisfaction gained no longer outweighs the extra cost.
The answer
The missing word is benefit — the concept is marginal benefit. Buying in bulk is advantageous only as long as the marginal benefit (the extra satisfaction or value you get from one more unit) is greater than or equal to the marginal cost (what that extra unit costs you). The point at which it is no longer advantageous to buy in bulk is where marginal benefit drops below marginal cost. Rationally, you keep buying additional units up to the quantity where marginal benefit = marginal cost, and stop there.
Why marginal benefit is the key idea
Every decision to buy "one more" is a marginal decision. Marginal benefit is the maximum you'd be willing to give up for one additional unit; marginal cost is what you actually give up to get it. As you buy more of the same good, the marginal benefit of each additional unit tends to fall — this is the law of diminishing marginal utility. The first case of bottled water is very valuable; the tenth case sitting in your garage is worth much less to you. Meanwhile the cost per additional unit does not fall as fast (and eventually storage, spoilage, and cash tied up push it up). Bulk buying is smart while the still-high marginal benefit exceeds the cost, but once that extra unit's benefit dips below its cost, buying more makes you worse off.
Why not the other options
- Marginal cost — this is the cost side of the comparison, not the point at which bulk buying stops paying off. The tipping point is defined by the benefit falling below cost, so the word that completes the idea of "no longer advantageous" is the benefit that has shrunk. Marginal cost is half the comparison, but it is not the term the sentence asks for.
- Marginal product — this measures the extra output produced by one more unit of an input (like an additional worker) in production, not the value a consumer gets from buying one more unit. It belongs to the theory of the firm, not to a buying-in-bulk consumption decision.
- Marginal revenue — this is the extra revenue a seller earns from selling one more unit. It applies to a producer's sales decision, not to your decision about whether to purchase in bulk.
A worked example
Suppose granola bars cost $0.50 each and you value them as follows: the first box is worth $6 to you, the second $4, the third $2.50, the fourth $1, and the fifth $0.40. If a bulk pack charges effectively $2 per box:
| Box | Marginal benefit | Marginal cost | Buy? |
|---|---|---|---|
| 1 | $6.00 | $2.00 | Yes |
| 2 | $4.00 | $2.00 | Yes |
| 3 | $2.50 | $2.00 | Yes |
| 4 | $1.00 | $2.00 | No |
| 5 | $0.40 | $2.00 | No |
You should buy three boxes. At the fourth box, marginal benefit ($1.00) falls below marginal cost ($2.00) — that is the exact point where bulk buying is no longer advantageous. The tipping point is governed by marginal benefit sinking beneath marginal cost.
The bigger picture
This is the general rule for any "how much" decision: continue while marginal benefit ≥ marginal cost, and stop where they meet. It explains why endless bulk buying is irrational despite the lower per-unit price — the discount is only worthwhile as long as you still get enough added value from each extra unit.
| 1 | $6.00 | $2.00 | Yes |
| 2 | $4.00 | $2.00 | Yes |
| 3 | $2.50 | $2.00 | Yes |
| 4 | $1.00 | $2.00 | No — benefit now below cost |
| 5 | $0.40 | $2.00 | No |
Frequently asked
What is marginal benefit?
Marginal benefit is the additional satisfaction, value, or usefulness you gain from consuming or buying one more unit of a good. It represents the maximum you would be willing to give up to obtain that extra unit, and it typically declines as you consume more.
What is the difference between marginal benefit and marginal cost?
Marginal benefit is the extra value you get from one more unit, while marginal cost is what that additional unit costs you. You should keep buying as long as marginal benefit is at least as large as marginal cost, and stop where the two are equal.
When should you stop buying in bulk?
Stop when the marginal benefit of the next unit falls below its marginal cost. Up to that point each extra unit adds more value than it costs; beyond it, the added value no longer justifies the expense, so buying more makes you worse off.
How do you calculate marginal benefit?
Marginal benefit is the change in total benefit divided by the change in quantity — essentially the value of one more unit. In practice it is the most you'd pay for that next unit, and it usually decreases with each additional unit due to diminishing marginal utility.
What is diminishing marginal utility?
Diminishing marginal utility is the principle that each additional unit of a good gives you less extra satisfaction than the previous one. It is why marginal benefit falls as you buy more, and why bulk buying eventually stops being worthwhile.