PTCB Pharmacy Math: Calculations You Need to Know for the PTCE

Calculations are still on the exam. Alligations are not.

PTCB marks several knowledge areas with an asterisk as calculation-based. The densest cluster is Order Entry statement 4.1: formulas, ratios, proportions, conversions, Sig codes, days supply, quantity, dose, concentration, and dilutions. Put those PTCE calculation setups into practice in Passy → with original numbers, not recalled exam items.

PTCB’s job analysis removed alligations from the calculations statement and removed nonsterile compounding knowledge areas. If a worksheet still opens with a tic-tac-toe alligation grid, it is teaching a previous outline. PTCB exam changes in 2026 is the official deletion list.

These examples are educational exam-prep setups. They are not instructions for a specific patient’s therapy.

Days supply from the Sig

Days supply = quantity dispensed ÷ quantity used per day.

Example. 90 tablets. Directions: 1 tablet by mouth twice daily.

Twice daily is 2 tablets each day. 90 ÷ 2 = 45 days.

Once daily would have been 90 days. Three times daily would have been 30 days. Decode the Sig before you divide. Order Entry & Processing is where b.i.d. and t.i.d. live as language.

Ratio-proportion for a liquid dose

Example. Label: 125 mg per 5 mL. Prescribed dose: 200 mg. Find milliliters.

125 mg / 5 mL = 200 mg / x mL
125x = 1,000
x = 8 mL

10 mL would be 250 mg. 5 mL is only 125 mg. Match milligrams to milligrams before you cross-multiply.

Household to metric

If the item gives 1 teaspoon = 5 mL, then 3 teaspoons = 15 mL. If it gives 1 ounce = 30 mL, then 2 ounces = 60 mL. Use the equivalent in the question. Do not import a second unofficial conversion into the same step.

Percent strength (w/v)

Example. 2 grams of drug in 50 mL of solution.

Percent w/v is grams per 100 mL.
2 g / 50 mL = x g / 100 mL
x = 4% w/v

That is a remaining concentration setup. It is not alligation of two stock bottles into a third strength.

Time and the on-screen calculator

PTCB Help Center calculator guidance describes an on-screen calculator. A personal calculator is not the default. Every extra tap comes out of the 110-minute exam clock. How long is the PTCB exam? is the timer. Practice moving on from a messy setup so one item does not consume three minutes.

PTCB / PTCE study guide is how math fits beside Domain 1. Mix calculation items with the other PTCE domains in Passy → after each worked example.

One messy days-supply item is not a reason to skip mixed domains the rest of the week.

Keep PTCE math reps in the Passy rotation → until the proportion is automatic.

Days supply, ratios, and conversions still share the 110-minute clock with Domain 1.

Plan the next session in Passy → if days supply is still the miss that slows the whole set.