Programming is applied math: percentages of a max, zones from a resting heart rate, macros from a goal. These are the exact formulas your certification taught — Epley, Karvonen, Mifflin-St Jeor — running at client-session speed.
Yes: the NSCA teaches Epley for 1RM estimation, NASM materials reference Brzycki, ACSM teaches the Karvonen heart-rate-reserve method, and Mifflin-St Jeor is the equation the Academy of Nutrition and Dietetics rates most accurate. Each tool page documents its formula.
Have them complete a crisp set of 5 at a challenging weight — never grind a true max with a new client. Enter weight and reps, then program straight off the percentage table: 5×5 work typically sits at 80–85% of the estimate.
That is the idea — no accounts, no app installs, works on any phone between sets. Many trainers put the macro and zone calculators in their onboarding packet; every tool also has a free embed snippet for your training site.