Everyday Calculators Guide: How to Calculate BMR, TDEE, BMI, Age & Work Hours

Everyday health, scheduling, and payroll calculations look simple on the surface, yet small formula mistakes—such as confusing resting BMR with active TDEE, or typing 8 hours 15 minutes into a payroll sheet as 8.15 instead of 8.25—lead to inaccurate nutrition targets and underpaid timesheets.

Here are the exact clinical and mathematical formulas behind seven everyday calculations and how to apply them accurately.

1. Health & Metabolism: BMI vs. BMR vs. TDEE

Body Mass Index (BMI)

Body Mass Index is a population-level screening ratio comparing body mass to height squared:

Under World Health Organization (WHO) adult classifications:

Check metric (kg/cm) or imperial (lb/ft-in) measurements instantly in the EverySolve BMI Calculator.

Basal Metabolic Rate (BMR — Mifflin-St Jeor Equation)

Your BMR is the minimum energy (in kilocalories per day) your body requires at complete physical and digestive rest to maintain breathing, circulation, cell repair, and core temperature. In clinical dietetics, the Mifflin-St Jeor (1990) equation is the validated reference standard:

• Men: BMR = (10 × Weight in kg) + (6.25 × Height in cm) - (5 × Age in years) + 5
• Women: BMR = (10 × Weight in kg) + (6.25 × Height in cm) - (5 × Age in years) - 161

Calculate your baseline resting metabolism with the EverySolve BMR Calculator.

Total Daily Energy Expenditure (TDEE)

Because nobody spends 24 hours motionless in bed, your actual daily maintenance calorie requirement (TDEE) multiplies your BMR by a physical activity factor:

• Sedentary (desk job, little exercise): BMR × 1.20
• Lightly Active (light exercise 1–3 days/week): BMR × 1.375
• Moderately Active (moderate exercise 3–5 days/week): BMR × 1.55
• Very Active (hard training 6–7 days/week): BMR × 1.725
• Extra Active (physical labor or 2× daily training): BMR × 1.90

Plan maintenance, deficit, or surplus targets using the EverySolve Calorie (TDEE) Calculator.

2. Time & Calendar Arithmetic

Date Difference & Business Working Days

Calculating elapsed days between two dates accurately requires parsing local calendar components (Year, Month, Day) so daylight saving time (DST) shifts do not introduce 23-hour or 25-hour rounding bugs, while properly counting every leap-year February 29th. When tracking contract notice periods or SLA deadlines, use the EverySolve Date Difference Calculator to separate total calendar days from Monday–Friday business working days.

Exact Chronological Age

Chronological age in years, months, and days borrows days from the preceding calendar month (accounting for 28, 29, 30, or 31-day month lengths). Compute exact age and next-birthday countdowns with the EverySolve Age Calculator.

Converting Shift Hours & Minutes to Decimal Hours for Payroll

Base-60 clock minutes cannot be multiplied directly by an hourly wage rate. Convert minutes into decimal hours by dividing minutes by 60:

• 15 minutes = 15 ÷ 60 = 0.25 hours
• 30 minutes = 30 ÷ 60 = 0.50 hours
• 45 minutes = 45 ÷ 60 = 0.75 hours

For example, an 8-hour 15-minute shift after deducting a 30-minute unpaid break equals 7 hours 45 minutes, or 7.75 decimal hours. Compute day and overnight shifts with the EverySolve Time Duration Calculator.

3. Dining & Group Bill Splitting

When splitting a restaurant bill among a group, calculate the tip percentage on the subtotal and divide the combined total evenly:

Split checks and custom tip percentages effortlessly at the table with the EverySolve Tip & Split Bill Calculator.