Supply Shift New Equilibrium Calculator

Enter the demand intercept and slope, the original supply intercept and slope, and the size of the supply shift. The calculator reports the original equilibrium, the shifted supply intercept, the new equilibrium, and the differences between them, making the direction and magnitude of the market adjustment explicit.

Describe the original demand and supply curves

Start by expressing demand as Qd = demand_intercept − demand_slope × price and supply as Qs = supply_intercept + supply_slope × price. The demand slope is entered as a positive absolute value even though price has a negative effect on quantity demanded in the equation. The supply slope must be nonnegative, representing an upward-sloping or perfectly vertical-in-quantity relationship in this quantity-as-a-function-of-price form. Intercepts are quantities at a price of zero and may be negative when a fitted line crosses the quantity axis outside the economically observed range. Keep all price and quantity units consistent. For example, if quantity is measured in thousands of units and price is dollars per unit, both intercepts and the supply shift must use thousands of units, while both slopes must represent thousands of units per dollar. The calculator first sets original quantity demanded equal to original quantity supplied. This establishes a baseline, so the effect reported later is attributable only to the specified parallel supply movement rather than to an unnoticed change in demand or slope convention.

Represent the parallel supply shift correctly

Enter the supply shift as a quantity added to supply at every price. A positive value shifts the curve to the right: producers supply more at each price, so the new supply intercept equals the original intercept plus the shift. A negative value shifts it to the left and reduces supply at each price. Because the movement is parallel, the supply slope does not change. This distinction matters. A change in slope represents a rotation of the curve and requires a different model; it cannot be summarized by one constant horizontal displacement. With demand held fixed, the calculator solves demand_intercept − demand_slope × price = supply_intercept + supply_shift + supply_slope × price. It then substitutes the resulting price into demand to obtain the shared equilibrium quantity. A rightward supply shift normally lowers equilibrium price and raises equilibrium quantity, while a leftward shift normally raises price and lowers quantity. A zero shift deliberately returns the baseline equilibrium and reports no directional movement, which is useful for checking data pipelines and spreadsheet formulas.

Interpret the result and check economic plausibility

The output separates the initial equilibrium from the new equilibrium and includes signed changes. A negative price change means the equilibrium price fell; a positive quantity change means equilibrium output rose. The shifted supply intercept is also returned so you can reconstruct the new curve or document the assumption used in a report. The arithmetic solves the linear equations exactly and rounds only the displayed numeric results to twelve decimal places for stable output. It does not impose price floors, capacity constraints, taxes, rationing, nonlinear behavior, or a requirement that price and quantity be positive. Consequently, a sufficiently large shift can produce a mathematically valid negative price or quantity. Treat that as a warning that the linear curves are being extrapolated beyond a meaningful market range, not automatically as a software error. Before using the estimate for a decision, confirm that both curves were fitted over a relevant interval, that the shift uses the same quantity unit as the intercepts, and that no simultaneous demand shift occurred. Automated requests cost $0.002; the deterministic calculation uses no network data or hidden assumptions.