NumLuma guides

Understand the number behind the answer.

Evergreen explanations for the calculations people actually use — written to add context, show the math and connect directly to practical tools.

Learn by topic

Short enough to use. Detailed enough to trust.

A practical guide to percentages, percentage change, discounts and common percent calculations.

Understand the difference between margin and markup, why they are not interchangeable, and how each is calculated.

Convert hourly, weekly, monthly and annual pay using consistent assumptions about hours and working weeks.

A practical framework for measuring area and volume, adding waste, and turning project dimensions into material quantities.

Learn how principal, rate, time and compounding frequency interact in compound-interest calculations.

Understand CPC, CPM, CTR and CPA, what each metric measures, and why no single advertising metric tells the whole story.

Learn how inventory turnover is calculated, how it relates to days inventory, and why context matters when comparing inventory efficiency.

A practical guide to turning an hourly billing rate into a project quote while accounting for billable hours, uncertainty and non-billable work.