https://numluma.com/ Evergreen explanations, worked questions, formulas and practical calculations from NumLuma. en https://numluma.com/guides/percentages-made-simple/ https://numluma.com/guides/percentages-made-simple/ A practical guide to percentages, percentage change, discounts and common percent calculations. Everyday math guide https://numluma.com/guides/profit-margin-vs-markup/ https://numluma.com/guides/profit-margin-vs-markup/ Understand the difference between margin and markup, why they are not interchangeable, and how each is calculated. Business guide https://numluma.com/guides/hourly-pay-vs-salary/ https://numluma.com/guides/hourly-pay-vs-salary/ Convert hourly, weekly, monthly and annual pay using consistent assumptions about hours and working weeks. Work guide https://numluma.com/guides/estimating-home-project-materials/ https://numluma.com/guides/estimating-home-project-materials/ A practical framework for measuring area and volume, adding waste, and turning project dimensions into material quantities. Home projects guide https://numluma.com/guides/compound-interest-basics/ https://numluma.com/guides/compound-interest-basics/ Learn how principal, rate, time and compounding frequency interact in compound-interest calculations. Money math guide https://numluma.com/guides/digital-ad-metrics-explained/ https://numluma.com/guides/digital-ad-metrics-explained/ Understand CPC, CPM, CTR and CPA, what each metric measures, and why no single advertising metric tells the whole story. Business guide https://numluma.com/guides/inventory-turnover-explained/ https://numluma.com/guides/inventory-turnover-explained/ Learn how inventory turnover is calculated, how it relates to days inventory, and why context matters when comparing inventory efficiency. Business guide https://numluma.com/guides/freelance-project-pricing-basics/ https://numluma.com/guides/freelance-project-pricing-basics/ A practical guide to turning an hourly billing rate into a project quote while accounting for billable hours, uncertainty and non-billable work. Work guide https://numluma.com/answers/how-much-house-can-i-afford/ https://numluma.com/answers/how-much-house-can-i-afford/ Use the monthly mortgage payment as a starting point for home affordability, then account separately for taxes, insurance, fees and your wider budget. Decision answer https://numluma.com/answers/how-long-to-pay-off-10000-debt/ https://numluma.com/answers/how-long-to-pay-off-10000-debt/ Estimate how long a $10,000 balance may take to pay off and how an extra monthly payment can change total interest and payoff time. Decision answer https://numluma.com/answers/what-profit-margin-should-i-charge/ https://numluma.com/answers/what-profit-margin-should-i-charge/ There is no universal right profit margin. Compare your current margin with a target and see the revenue or cost change required to reach it. Decision answer https://numluma.com/answers/how-much-should-i-save-every-month/ https://numluma.com/answers/how-much-should-i-save-every-month/ Work backward from a savings goal and deadline to estimate the monthly amount required, using your current savings as the starting point. Decision answer https://numluma.com/answers/is-4x-roas-good/ https://numluma.com/answers/is-4x-roas-good/ Understand what 4x ROAS means, why it is not automatically profitable, and calculate the revenue required for 4x return on ad spend. Decision answer https://numluma.com/answers/how-much-is-25-an-hour-per-year/ https://numluma.com/answers/how-much-is-25-an-hour-per-year/ Convert a $25 hourly rate into weekly, monthly and annual gross pay using your actual hours and paid working weeks. Decision answer https://numluma.com/answers/how-much-paint-do-i-need-for-a-room/ https://numluma.com/answers/how-much-paint-do-i-need-for-a-room/ Estimate paint quantity from wall dimensions, coats, coverage and openings instead of guessing from room floor area. Decision answer https://numluma.com/answers/how-big-should-my-emergency-fund-be/ https://numluma.com/answers/how-big-should-my-emergency-fund-be/ Turn a chosen number of months of essential expenses into a concrete emergency-fund target. Decision answer https://numluma.com/answers/what-is-20-percent-off-150/ https://numluma.com/answers/what-is-20-percent-off-150/ Calculate the discount amount and final price for a 20% discount on $150, then change the values for any sale. Decision answer https://numluma.com/answers/how-much-should-i-charge-as-a-freelancer/ https://numluma.com/answers/how-much-should-i-charge-as-a-freelancer/ Estimate a sustainable freelance hourly rate from income goals, billable hours, expenses and non-billable time. Decision answer https://numluma.com/answers/how-much-will-10000-grow-in-10-years/ https://numluma.com/answers/how-much-will-10000-grow-in-10-years/ See how compound growth changes a $10,000 starting balance over 10 years at a chosen annual rate. Decision answer https://numluma.com/answers/how-much-will-my-road-trip-cost-in-gas/ https://numluma.com/answers/how-much-will-my-road-trip-cost-in-gas/ Estimate trip fuel cost from distance, fuel economy and fuel price. Decision answer https://numluma.com/answers/how-much-flooring-do-i-need/ https://numluma.com/answers/how-much-flooring-do-i-need/ Estimate flooring quantity from room area, package coverage and a waste allowance. Decision answer https://numluma.com/answers/what-markup-do-i-need/ https://numluma.com/answers/what-markup-do-i-need/ Compare product cost with selling price to understand markup and how it differs from profit margin. Decision answer https://numluma.com/answers/how-much-will-a-25000-loan-cost-per-month/ https://numluma.com/answers/how-much-will-a-25000-loan-cost-per-month/ Estimate the monthly payment for a $25,000 fixed-rate loan using the interest rate and loan term. Decision answer https://numluma.com/answers/what-is-20-percent-of-150/ https://numluma.com/answers/what-is-20-percent-of-150/ See how to calculate 20% of 150 and use the same method for any percentage-of-a-number question. Decision answer https://numluma.com/answers/how-much-is-a-5-percent-raise/ https://numluma.com/answers/how-much-is-a-5-percent-raise/ Calculate the new pay after a 5% raise and see the dollar increase from your current salary or wage. Decision answer https://numluma.com/answers/how-much-should-my-emergency-fund-be/ https://numluma.com/answers/how-much-should-my-emergency-fund-be/ Turn a chosen number of months of essential expenses into an emergency-fund target you can inspect and adjust. Decision answer https://numluma.com/answers/how-much-should-i-charge-for-freelance-work/ https://numluma.com/answers/how-much-should-i-charge-for-freelance-work/ Work backward from an income goal, billable hours and business costs to estimate a freelance hourly rate. Decision answer https://numluma.com/answers/how-many-units-to-break-even/ https://numluma.com/answers/how-many-units-to-break-even/ Calculate break-even units from fixed costs, selling price and variable cost per unit, then test a target profit. Decision answer https://numluma.com/answers/how-much-is-30-percent-off/ https://numluma.com/answers/how-much-is-30-percent-off/ Calculate a 30% discount, the amount saved and the final sale price for any original price. Decision answer https://numluma.com/answers/how-much-tip-on-50/ https://numluma.com/answers/how-much-tip-on-50/ Calculate common tip percentages on a $50 bill and see the final total. Decision answer https://numluma.com/answers/how-much-will-compound-interest-grow/ https://numluma.com/answers/how-much-will-compound-interest-grow/ Estimate how a starting balance can grow over time with compounding and optional recurring contributions. Decision answer https://numluma.com/answers/how-much-does-a-road-trip-cost-in-gas/ https://numluma.com/answers/how-much-does-a-road-trip-cost-in-gas/ Estimate trip fuel cost from distance, vehicle fuel economy and fuel price. Decision answer https://numluma.com/answers/how-much-concrete-do-i-need/ https://numluma.com/answers/how-much-concrete-do-i-need/ Estimate concrete volume from length, width and depth, then convert the result into cubic yards for ordering. Decision answer https://numluma.com/answers/how-much-revenue-for-4x-roas/ https://numluma.com/answers/how-much-revenue-for-4x-roas/ Calculate the revenue required to reach a 4x ROAS at any advertising spend level. Decision answer https://numluma.com/formulas/percentage-formula/ https://numluma.com/formulas/percentage-formula/ Learn the percentage formula, how to find X% of a number, how to reverse a percentage, and how the variables relate. Formula reference https://numluma.com/formulas/percentage-change-formula/ https://numluma.com/formulas/percentage-change-formula/ Understand the percentage increase and decrease formula from an original value to a new value. Formula reference https://numluma.com/formulas/profit-margin-formula/ https://numluma.com/formulas/profit-margin-formula/ Learn the profit margin formula, the difference between profit and margin, and how revenue and cost affect the result. Formula reference https://numluma.com/formulas/markup-formula/ https://numluma.com/formulas/markup-formula/ Learn the markup formula and why markup percentage is different from profit margin. Formula reference https://numluma.com/formulas/break-even-formula/ https://numluma.com/formulas/break-even-formula/ Learn the break-even units formula using fixed costs, selling price and variable cost per unit. Formula reference https://numluma.com/formulas/roi-formula/ https://numluma.com/formulas/roi-formula/ Learn the return on investment formula and how gain or loss is measured relative to the amount invested. Formula reference https://numluma.com/formulas/roas-formula/ https://numluma.com/formulas/roas-formula/ Learn the return on ad spend formula and how attributed revenue relates to advertising spend. Formula reference https://numluma.com/formulas/cagr-formula/ https://numluma.com/formulas/cagr-formula/ Learn the compound annual growth rate formula for converting beginning value, ending value and time into an annualized growth rate. Formula reference https://numluma.com/formulas/compound-interest-formula/ https://numluma.com/formulas/compound-interest-formula/ Learn the compound interest formula using principal, annual rate, compounding frequency and time. Formula reference https://numluma.com/formulas/simple-interest-formula/ https://numluma.com/formulas/simple-interest-formula/ Learn the simple interest formula for principal, annual rate and time. Formula reference https://numluma.com/formulas/mortgage-payment-formula/ https://numluma.com/formulas/mortgage-payment-formula/ Understand the fixed-rate mortgage principal-and-interest payment formula and the variables behind the monthly payment. Formula reference https://numluma.com/formulas/loan-payment-formula/ https://numluma.com/formulas/loan-payment-formula/ Learn the fixed-payment loan formula used for amortizing installment loans. Formula reference https://numluma.com/formulas/hourly-to-salary-formula/ https://numluma.com/formulas/hourly-to-salary-formula/ Learn how hourly rate, hours per week and working weeks per year combine into estimated annual gross pay. Formula reference https://numluma.com/formulas/discount-formula/ https://numluma.com/formulas/discount-formula/ Learn how to calculate discount amount, sale price and percent off from an original price. Formula reference https://numluma.com/formulas/average-formula/ https://numluma.com/formulas/average-formula/ Learn the arithmetic mean formula and how sum and count determine the average of a set of numbers. Formula reference