Desmos on the SAT: How to Use the Built-In Calculator

The Digital SAT has a Desmos graphing calculator built into the Bluebook testing app, and you can use it on every Math question. Students who know it well solve many problems in a few clicks that would take minutes by hand. Students who meet it for the first time on test day lose time instead. Here is what you get and how to use it.

The calculator rules in short

• The Desmos calculator is available for the entire Math section, in both modules.
• You can switch between the graphing and scientific versions at any time.
• There is no calculator in Reading and Writing, built in or your own.
• You may also bring your own approved handheld calculator. Calculators with computer algebra systems (CAS) are not allowed, and you must clear any saved programs or formulas.
• If your own calculator fails during testing, you can continue with the built-in Desmos.

Most students do not need to bring a calculator at all. If you do, bring one you have practiced with, not a new one.

Five ways Desmos saves time

1. Solve an equation by graphing both sides

Type the left side and the right side as two separate entries, for example y = 3x + 7 and y = 22. Click the point where the lines cross. The x value is your solution. This works for equations you would rather not rearrange by hand, including ones with fractions, absolute values or exponents.

2. Solve a system of equations

Enter both equations exactly as written. Desmos accepts forms like 2x + 3y = 12 without solving for y first. Click the intersection to read off both values. If the lines never cross, the system has no solution; if they lie on top of each other, it has infinitely many.

3. Find zeros, the vertex and the y intercept of a quadratic

Type the function, such as y = x^2 - 6x + 5, and click the curve. Desmos marks the key points in gray. Click them to see the x intercepts (1 and 5 here), the vertex at (3, -4) and the y intercept. Questions about the minimum value, the axis of symmetry or the number of real solutions become a quick look at the graph.

4. Use a slider for an unknown constant

When a question says something like "for what value of k does the equation have exactly one solution", type the expression with k in it. Desmos offers to add a slider. Drag it and watch when the graph touches the line exactly once. Then confirm the value by checking it in the original equation.

5. Check an answer you found by hand

Even when you solve algebraically, graph the result. Plugging an answer choice into Desmos takes a few seconds and catches sign errors, which are among the most common reasons for lost Math points.

When not to reach for Desmos

Desmos is not always faster. Simple arithmetic, one step equations and many geometry questions are quicker on scratch paper. Word problems still require you to build the right equation first: the calculator cannot read the question for you. A good habit is to decide in the first ten seconds whether a question is a graphing question or a pencil question.

The reference sheet

Next to the calculator, Bluebook gives you a reference sheet with common geometry formulas such as area, volume and the special right triangles. It does not include everything. Algebra rules, the quadratic formula, slope and the equation of a circle are not on it. Our SAT formula sheet lists what is given and what you need to memorize.

How to practice with Desmos

1. Use the free calculator at desmos.com, which works the same way as the one in Bluebook.
2. Take at least one full practice test in the Bluebook app so the layout and the calculator window feel familiar.
3. When you review a Math mistake, ask whether graphing would have caught it, and redo the question with Desmos.

Most of the Math section is algebra, so graphing skills pay off on a large share of questions. See which topics appear most often in our guide to SAT Math topics.