Equilibrium Price
What is Equilibrium Price?
The equilibrium price is the price at which quantity demanded equals quantity supplied.
The equilibrium price is the price that balances the quantity demanded by consumers with the quantity supplied by producers. At this price, the market is in equilibrium, and there are no shortages or surpluses. The equilibrium price is determined by the intersection of the demand and supply curves.
Equilibrium Price: a worked example
Take Qd = 300 minus 10P and Qs = 20P minus 60, with P in dollars and Q in units per day. Equilibrium requires 300 minus 10P = 20P minus 60, so 360 = 30P and P = $12. Substituting back, Qd = 300 minus 120 = 180 and Qs = 20 times 12 minus 60 = 180, which confirms the answer. Now test a price of $15. Quantity demanded is 300 minus 150 = 150 while quantity supplied is 20 times 15 minus 60 = 240, a surplus of 90 units that pressures sellers to cut price. Test $9 instead: quantity demanded is 300 minus 90 = 210 while quantity supplied is 20 times 9 minus 60 = 120, a shortage of 90 units that lets sellers raise price. Only at $12 does the pressure disappear from both sides, and that is exactly what equilibrium means.
The mistake students make with equilibrium price
Two mechanical errors cost points. The first is equating mismatched forms: if demand arrives as P = 30 minus 0.1Q while supply arrives as Qs = 20P minus 60, setting those two expressions equal solves nothing. Convert both to the same variable first, then equate them. The second is reporting equilibrium quantity as the sum of quantity demanded and quantity supplied. At equilibrium those two are the same number, so the answer is 180 units, not 360. Equilibrium quantity is one number playing both roles at once.
Equilibrium Price questions
How do you calculate the equilibrium price?
Equilibrium price comes from setting quantity demanded equal to quantity supplied and solving for P. With Qd = 300 minus 10P and Qs = 20P minus 60, the equation 300 minus 10P = 20P minus 60 gives 360 = 30P, so P = $12. Always substitute that price back into both equations as a check, since matching quantities confirm the algebra. If either equation is written in inverse form with P alone on the left, rearrange before equating.
What happens when price is above equilibrium?
A price above equilibrium creates a surplus, because quantity supplied exceeds quantity demanded. Unsold inventory builds up, and sellers respond by cutting price, which draws buyers back and discourages some production until the gap closes. The market slides down to equilibrium on its own unless a binding price floor holds the price up by law. Below equilibrium the reverse happens: a shortage forms, and competition among buyers bids the price back up.
Does the equilibrium price change when both curves shift?
Equilibrium price becomes indeterminate whenever the two shifts push it in opposite directions. If demand rises and supply rises, quantity clearly increases, but price depends on which shift is larger, so the correct exam answer is indeterminate unless relative magnitudes are stated. When demand rises and supply falls, price clearly increases while quantity becomes the indeterminate variable. Naming which variable is certain and which is not earns the point.
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Related terms
Common comparisons
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