---
title: "Short-Run Supply | Intermediate Microeconomic Theory"
description: "Short-run supply is the quantity firms will produce with fixed capacity and some variable inputs, showing how competitive firms respond to price in Micro."
canonical: "https://fiveable.me/intermediate-microeconomic-theory/key-terms/short-run-supply"
type: "key-term"
subject: "Intermediate Microeconomic Theory"
unit: "Unit 3"
---

# Short-Run Supply | Intermediate Microeconomic Theory

## Definition

Short-run supply is the quantity a firm is willing and able to produce with some inputs fixed and some variable. In Intermediate Microeconomic Theory, it shows how competitive firms choose output before they can fully adjust plant size or other capacity.

## What It Is

Short-run supply is the amount a firm is willing and able to sell when some of its production inputs are fixed. In Intermediate Microeconomic Theory, this usually means the firm can change labor, materials, or other variable inputs, but not things like plant size, land, or major equipment right away.

That time limit matters. A factory cannot instantly build a new building just because demand rises, and it cannot instantly shut down its fixed capital without taking time and money. So the firm’s short-run output choice is based on the current technology and cost structure it already has.

For a competitive firm, short-run supply comes from the part of the marginal cost curve that lies above average variable cost. If market price is high enough to cover variable cost, the firm produces. If price falls below average variable cost, it is better off shutting down for the moment because producing would lose even more money than stopping.

This is why short-run supply is tied to profit maximization. The firm chooses the output level where price equals marginal cost, as long as the firm can cover variable cost. If price is above average total cost, the firm earns profit. If price is between average total cost and average variable cost, the firm still produces in the short run even though it takes an operating loss, because shutting down would be worse.

A simple way to picture it is this: the firm is not asking, "What would my business look like if I rebuilt everything?" It is asking, "Given the plant I already have, how much should I make today?" That is why short-run supply is a temporary response to market price, not a permanent statement about what the firm could produce after it has time to adjust all inputs.

Short-run supply also moves when input costs change. If wages or materials rise, marginal cost rises and the firm supplies less at each price. If those costs fall, short-run supply shifts outward. In problem sets, this usually shows up as a comparison of output choices under different prices, costs, or fixed-capacity conditions.

## Why It Matters

Short-run supply is the bridge between firm theory and market outcomes. It shows how a competitive firm turns its cost curve into an output choice, which is exactly the kind of reasoning used in profit maximization problems. If you can trace short-run supply, you can explain why a firm keeps producing during a loss, why it shuts down, and how a change in price changes quantity supplied.

It also connects individual behavior to market equilibrium. When many firms each decide how much to produce in the short run, their choices add up to market supply. That is why short-run supply is part of the process that moves market price after a demand shift. In a class problem, you may be asked to predict whether the market clears at a higher price, lower price, or with some firms temporarily exiting production.

The concept also helps you separate short-run responses from long-run adjustments. In the short run, firms work with the capacity they already have. In the long run, they can enter, exit, expand, or shrink plants. Without that distinction, it is easy to misread a supply curve or assume every price change leads to full adjustment right away.

## Connections

### Marginal Cost

Short-run supply for a competitive firm is built from marginal cost, not from total cost. The firm produces up to the point where price equals marginal cost, but only on the part of the curve above average variable cost. When you graph supply, MC is the curve you are really reading to find the quantity response.

### [Cost Function](/intermediate-microeconomic-theory/key-terms/cost-function)

The cost function tells you how a firm’s total cost changes with output, fixed inputs, and variable inputs. Short-run supply comes from that cost structure because fixed costs are sunk in the short run, while variable costs affect the shutdown decision. If the cost function shifts, the short-run supply curve shifts too.

### [price-taking behavior](/intermediate-microeconomic-theory/key-terms/price-taking-behavior)

Short-run supply in perfect competition assumes the firm is a price taker. That means the market sets price, and the firm chooses quantity, not the other way around. If a firm could influence price, the supply decision would not follow the same marginal cost rule in the same clean way.

### [Profit Function](/intermediate-microeconomic-theory/key-terms/profit-function)

The profit function helps you check whether producing in the short run is better than shutting down. A firm may still produce with negative profit if it is covering variable cost, because fixed costs must be paid either way. That distinction shows up a lot in shutdown and operating decisions.

## On the AP Exam

A problem set question will usually give you a price, cost curves, or a table of output costs and ask for the firm’s quantity supplied in the short run. Your job is to compare price with marginal cost and check whether price is above average variable cost. If it is, the firm produces where P = MC on the upward-sloping part of MC. If price falls below average variable cost, the correct answer is shutdown, not a small positive output.

You may also be asked to interpret a graph. Look for the marginal cost curve above AVC, since that segment is the firm’s short-run supply curve. If input costs rise, describe the supply curve shifting left, and if demand rises, explain that the market price may rise even though the firm’s own short-run supply rule stays the same. On essay or discussion questions, use short-run supply to explain why firms can keep producing during a temporary downturn.

## Short-run supply vs Market Equilibrium

Short-run supply is the firm side of the story, while market equilibrium is the market-wide outcome where supply and demand meet. A firm’s short-run supply tells you how one competitive producer responds to price. Market equilibrium tells you the price and quantity for the whole market after all firms and buyers are accounted for.

## Key Takeaways

- Short-run supply is the quantity a firm will produce when some inputs are fixed and it cannot fully adjust capacity yet.
- For a competitive firm, short-run supply comes from marginal cost above average variable cost.
- A firm may keep producing at a loss in the short run if price still covers variable cost.
- If price falls below average variable cost, shutdown is better than producing more units.
- Short-run supply is temporary, while long-run supply reflects full adjustment of inputs and entry or exit.

## FAQs

### What is short-run supply in Intermediate Microeconomic Theory?

Short-run supply is the amount of output a firm is willing and able to produce when some inputs are fixed and only variable inputs can change. In competitive markets, it comes from the firm’s marginal cost curve above average variable cost. That makes it a temporary production choice, not a full long-run capacity decision.

### How do you find short-run supply for a competitive firm?

Start with the marginal cost curve, then use the part above average variable cost as the supply curve. The firm produces where price equals marginal cost, as long as price is high enough to cover variable cost. If price is below average variable cost, the firm shuts down.

### Why would a firm produce if it is making a loss in the short run?

Because fixed costs still have to be paid whether the firm produces or not. If the firm’s price covers variable costs, producing can reduce the loss compared with shutting down. The shutdown rule is about variable cost, not total profit alone.

### Is short-run supply the same as market supply?

Not exactly. Short-run supply describes one firm’s output choice given its current plant and cost conditions. Market supply is the sum of many firms’ short-run supplies. Market supply can shift when prices, costs, or the number of firms change.

## Related Study Guides

- [3.2 Profit maximization and the competitive firm's supply curve](/intermediate-microeconomic-theory/unit-3/profit-maximization-competitive-firms-supply-curve/study-guide/IHc5z7uGtxHlYuEW)

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