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Health & Fitness
Reddit-sourced calculators and references for the r/Fitness, r/loseit, r/GainIt, r/running, r/weightroom, r/Stronglifts, and r/sleep crowd — BMI, water intake, body-fat % (Navy), ideal weight, waist-to-hip, TDEE, calorie burn, protein requirement, macro split, HR zones (Karvonen), max HR (Tanaka), pace conversion, VO2max from 5K, 1RM (Epley/Brzycki), plate calculator, RPE → %1RM, warm-up sets, sleep cycle, caffeine half-life, sleep debt, training pace zones, race time predictor, and race splits.
53 tools available
Body Composition
BMI, body-fat % (Navy method), lean body mass, ideal weight, waist-to-hip ratio, and water-intake math that powers the r/loseit, r/Fitness, and r/GainIt body-composition threads.
Nutrition
TDEE, calorie-burn, macro split, and protein requirement by body weight for the r/Fitness, r/MealPrepSunday, and r/EatCheapAndHealthy nutrition debates.
Cardio & Zones
Max HR (Tanaka), Karvonen heart-rate zones, pace ↔ speed conversion, and VO2max from 5K time for r/running, r/cycling, and r/Rowing.
Strength Training
One-rep max (Epley / Brzycki / Lombardi), barbell plate-loading, RPE → %1RM, and warm-up set math that backs r/weightroom and r/Stronglifts progressions.
Sleep & Recovery
90-minute sleep cycle planner, caffeine half-life, and sleep-debt calculator that builds on the existing r/Fitness and r/sleep threads.
Wind Chill Calculator
Compute the felt-air temperature from wind speed and air temperature.
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BMI Calculator
Calculate Body Mass Index and see healthy ranges.
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Daily Water Intake Calculator
Get a personalized daily water target based on weight, activity, and climate.
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Body Fat % Calculator (Navy Method)
Estimate body-fat percentage from tape measurements and BMI.
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Ideal Weight Calculator (Devine / Hamwi / Robinson)
Compare the popular clinical ideal-weight formulas.
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Waist-to-Hip Ratio Calculator
Compute waist-to-hip ratio and the WHO health-risk band.
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TDEE & Macro Calculator
Calculate how many calories you burn per day and how to split them into protein, carbs, and fat.
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Calorie Burn Calculator
Estimate calories burned during exercise using MET formulas.
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Daily Protein Requirement Calculator
Get a protein target in g/day from body weight, lean mass, and activity.
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Macro Splitter (Carbs / Fat / Protein)
Split a calorie target into carbs, fat, and protein grams.
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Max Heart Rate Calculator (Tanaka)
Estimate HRmax from age with the Tanaka formula.
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Heart Rate Zone Calculator (Karvonen)
See your 5 training zones from resting HR and HRmax.
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Pace Converter (min/km ↔ min/mi ↔ km/h ↔ mph)
Convert running pace between metric and imperial units.
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VO2max Estimator from 5K Time
Estimate VO2max and equivalent race times from a recent 5K.
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One-Rep Max Calculator (Epley / Brzycki / Lombardi)
Estimate your 1RM from a sub-maximal set.
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Barbell Plate Loading Calculator
See exactly which plates to load on each side of the bar.
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RPE to %1RM Calculator
Convert Rate of Perceived Exertion to %1RM.
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Warm-Up Set Calculator
Build a smart warm-up ramp to your working sets.
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Sleep Cycle Calculator
Find the best bedtime or wake time based on 90-min sleep cycles.
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Caffeine Half-Life Calculator
Find out how much caffeine is still in your system at bedtime.
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Sleep Debt Calculator
See how much sleep debt you've accumulated and when you'll recover.
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Heat Index Calculator (NWS Rothfusz)
Get the felt-air temperature from heat and humidity.
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Running Pace Zones Calculator
Get easy / tempo / threshold / interval / repetition paces from a recent race or threshold pace.
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Race Time Predictor (Riegel)
Predict your 5K / 10K / half / marathon time from any other race result.
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Race Splits Calculator
Get per-mile or per-km splits to hit a goal finish time.
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Boston Qualifier Pace Calculator
What pace do you need for a Boston Qualifier at your age and gender?
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Labor Probability Estimator
Estimate the chance you'll go into labor this week.
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Heart-Rate Zone Calculator
Set Karvonen or Tanaka HR zones from age and resting HR.
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Race Time Predictor
Predict your finish time for any distance from a recent race.
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Maternity Benefit Net Pay
Estimate your net maternity benefit after the annualised tax rule.
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Cycle-Adjusted Due Date
Compute the EDD from LMP + cycle length or from a known conception date.
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NIPT False Positive Risk
What's the chance a 'high-risk' NIPT result is actually a false positive?
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First-Year Baby Cost Estimator
Estimate the total first-year cost of a baby in your city.
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Home Gym vs Gym Membership Calculator
Compare a home gym investment against monthly gym membership costs.
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Swimming Pace Calculator
Convert swim distance and time into per-100m pace, speed, and split times.
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Bicycle Gear Inches Calculator
Calculate gear inches, development, and cadence-speed for any chainring and cog.
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Protein Cost per Gram Calculator
Compare the price of protein sources by cost per gram of protein.
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GLP-1 Medication Cost Calculator
Estimate monthly and yearly GLP-1 medication costs from price, coupon, and insurance.
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Shift Work Sleep Schedule Calculator
Plan a sleep schedule that fits rotating or night-shift hours.
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Nicotine Cost Calculator
Estimate how much smoking or vaping costs per day, year, and lifetime.
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Therapy Cost Calculator
Estimate therapy session costs with insurance, sliding scale, or self-pay.
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IVF Cost Estimator
Estimate IVF cycle costs from clinic, medication, testing, and insurance.
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Invisalign Cost Calculator
Estimate Invisalign or clear aligner treatment from case complexity.
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Meal Prep Cost Per Serving Calculator
Calculate grocery cost per meal, batch cost, waste, and weekly budget.
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Monthly Supplement Cost Calculator
Calculate monthly supplement spend from price, servings, and frequency.
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Hearing Aid Cost Calculator
Compare hearing aid devices, fitting, follow-up, warranty, and financing.
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Urgent Care vs ER Cost Calculator
Compare urgent care and emergency department out-of-pocket costs.
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Cold Plunge Cost Calculator
Estimate a cold plunge tub, chiller, installation, and running cost.
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Weight Loss Timeline Calculator
Estimate how long reaching a weight goal takes with plateaus.
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Keto Macro Calculator
Calculate keto macros and monthly keto food cost.
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Maintenance Calories Calculator
Calculate maintenance calories and a safe deficit for weight goals.
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Baby Growth Percentile Calculator
Check baby weight and growth percentiles against WHO data.
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Fasting Window Calculator
Find a fasting window that fits your schedule and goals.
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