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Formulas & sources

Every CalcuPaw calculator uses one shared, tested formula library. The numbers below are the exact values in our code, each tied to the source it comes from.

  • 74calculators
  • 23sources
  • 13life-stage factors

The energy formula

Feeding calculators start from the resting energy requirement (RER), then multiply by a factor for life stage and activity.

RER=70×body weight (kg)0.75kcal / day

Energy needs are not a straight line with body weight, which is why weight is raised to the power 0.75. Sources: NRC 2006 · WSAVA Global Nutrition Guidelines · Merck Veterinary Manual.

Dog factors × RER

  • Neutered/spayed adult1.6
  • Intact (not neutered) adult1.8
  • Inactive or gains weight easily1.4
  • Weight loss (enter IDEAL weight)1
  • Active / light work2
  • Working / moderate work3
  • Puppy under 4 months3
  • Puppy 4 months to adult2

Cat factors × RER

  • Neutered/spayed adult1.2
  • Intact (not neutered) adult1.4
  • Inactive or gains weight easily1
  • Weight loss (enter IDEAL weight)0.8
  • Kitten (growing)2.5

Key constants

Every number is defined once in our code and cited here.

  • Treat limit10%

    Treats should stay under this share of daily calories.

    WSAVA / AAHA
  • Dog water intake50mL/kg/day

    Typical range 40–60. Above 100 mL/kg/day, see a vet.

    Merck Vet Manual
  • Body condition10%per point

    Each point above 5/9 is about this much over ideal weight.

    Laflamme 1997
  • Dog pregnancy63days

    From mating (normal 58–68); 65 days from the LH surge.

    Merck Vet Manual
  • Cat pregnancy63–65days

    Normal window 61–69 days from mating.

    Merck Vet Manual
  • Modified Atwater3.5 · 8.5 · 3.5kcal/g

    Protein · fat · carbohydrate energy factors.

    NRC 2006

Formula by calculator

The exact steps behind each result.

  • Cat Age Calculator
    1. Year 1 = 15, year 2 = 24, then +4 per year
    2. life stages: kitten <1, young adult 1–6, mature 7–10, senior >10
    AAFP_LSAAFP_LS10
  • Cat Food Calculator
    1. RER (kcal/day) = 70 × BW(kg)^0.75
    2. MER = RER × (neutered adult 1.2, intact 1.4, inactive/obese-prone 1.0)
    3. wet/dry split by % of MER
    NRC06WSAVA_NMERCK
  • Cat Pregnancy Due Date Calculator
    1. Gestation ≈ 63–65 days (normal range ~61–69)
    MERCK
  • Cost of Owning a Dog Calculator
    1. first year = one-off costs + 12 × monthly cost
    2. each later year = 12 × monthly cost
    3. lifetime = one-off costs + 12 × monthly cost × expected lifespan (years). All values are the ones you enter.
    MATHMCM24
  • Dog Age Calculator
    1. Size-based chart: year 1 ≈ 15, year 2 ≈ 24, then +4 (small) / +5 (medium) / +6–7 (large/giant) per year
    2. also show epigenetic formula human = 16 × ln(dog age) + 31 (Wang 2020, Labradors)
    AAHA_LSWANG20INDUSTRY
  • Dog Body Condition Score & Ideal Weight Calculator
    1. WSAVA 9-point BCS
    2. each point above 5 ≈ 10% over ideal: ideal weight = current ÷ (1 + 0.10 × (BCS − 5))
    WSAVA_NLAF97
  • Dog Calorie Calculator
    1. RER (kcal/day) = 70 × BW(kg)^0.75
    2. MER = RER × life-stage factor (table shown on page, NRC/Merck)
    NRC06MERCK
  • Dog Crate Size Calculator
    1. Crate length ≈ body length + 5–10 cm (2–4 in)
    2. height ≈ standing height to top of head/ears + 5–10 cm
    AKC_GINDUSTRY
  • Dog Food Calculator
    1. RER (kcal/day) = 70 × BW(kg)^0.75
    2. MER = RER × factor (neutered adult 1.6, intact 1.8, inactive/obese-prone 1.2–1.4, light work 2.0, moderate 3.0)
    3. grams/day = MER ÷ (kcal per kg ÷ 1000)
    4. cups = MER ÷ kcal per cup
    NRC06WSAVA_NMERCK
  • Dog Food Calorie
    1. Modified Atwater: kcal/100 g = 3.5×protein + 8.5×fat + 3.5×NFE
    2. NFE = 100 − (protein+fat+fibre+moisture+ash)
    3. ×10 → kcal/kg
    NRC06AAFCO
  • Dog Harness Size Calculator
    1. Measure widest chest girth
    2. map to size bands and ALWAYS defer to brand chart (no universal standard)
    INDUSTRY
  • Dog Heat Cycle Calculator
    1. Interoestrous interval average ~7 months (range 4–12, smaller breeds more often)
    2. proestrus ≈ 9 days, oestrus ≈ 9 days
    MERCK
  • Dog Pregnancy Due Date Calculator
    1. Due ≈ 63 days from ovulation (65 ± 1 from LH surge)
    2. from mating 58–68 days. The calculator shows the due date plus the earliest and latest normal dates.
    MERCK
  • Dog Treat Calorie Calculator
    1. MER = 70 × BW(kg)^0.75 × life-stage factor
    2. treat allowance (kcal/day) = 10% of MER
    3. treats allowed = floor(0.10 × MER ÷ kcal per treat)
    WSAVA_NAAHA_WM
  • Dog Water Intake Calculator
    1. Maintenance ≈ 50 mL per kg per day (range ~40–60)
    2. >100 mL/kg/day = possible polydipsia → see a vet
    MERCK
  • Dog Weight Loss Calculator
    1. Daily kcal = 1.0 × RER(ideal weight)
    2. safe loss 1–2% body weight/week → weeks = ln(ideal/current) ÷ ln(1 − rate)
    AAHA_WMWSAVA_N
  • Dry Matter Basis Calculator
    1. Nutrient on DM basis (%) = as-fed % ÷ (100 − moisture %) × 100
    AAFCONRC06
  • Kitten Food Calculator
    1. RER (kcal/day) = 70 × BW(kg)^0.75
    2. MER = RER × 2.5 until ~12 months
    3. split into 3–4 meals
    NRC06MERCK
  • Puppy Food Calculator
    1. RER (kcal/day) = 70 × BW(kg)^0.75
    2. MER = RER × 3.0 (<4 months) or × 2.0 (4 months → adult)
    3. portion = MER ÷ food kcal density
    NRC06WSAVA_NMERCK
  • Raw Dog Food Calculator
    1. Adult daily raw = 2–3% of ideal body weight
    2. puppy = 2–3% of EXPECTED adult weight (or 5–10% of current, whichever lower)
    3. split by chosen ratio (muscle/bone/liver/other organ). Cross-check kcal vs MER
    NRC06PRACTICE
  • Cat Calorie Calculator
    1. RER (kcal/day) = 70 × BW(kg)^0.75
    2. MER = RER × factor (neutered adult 1.2, intact 1.4, inactive/obese-prone 1.0, weight loss 0.8 × RER of ideal weight)
    NRC06MERCKWSAVA_N
  • Cat Treat Calorie Calculator
    1. MER = 70 × BW(kg)^0.75 × life-stage factor
    2. treat allowance (kcal/day) = 10% of MER
    3. treats allowed = floor(0.10 × MER ÷ kcal per treat)
    WSAVA_NAAHA_WM
  • Dog Food Cost Calculator
    1. grams/day = MER ÷ (kcal per kg ÷ 1000)
    2. cost/day = grams/day ÷ 1000 × (bag price ÷ bag kg)
    3. month = day × 365/12
    4. year = day × 365
    5. days per bag = bag grams ÷ grams/day
    NRC06WSAVA_NMERCKMATH
  • Dog Food Cups to Grams Calculator
    1. grams per cup = kcal per cup ÷ (kcal per kg ÷ 1000)
    2. grams = cups × grams per cup
    MATH
  • Cost of Owning a Cat Calculator
    1. first year = one-off costs + 12 × monthly cost
    2. each later year = 12 × monthly cost
    3. lifetime = one-off costs + 12 × monthly cost × expected lifespan (years). All values are the ones you enter.
    MATHTENG24
  • Puppy & Kitten Age Calculator
    1. age in days = as-of date − birth date
    2. weeks = floor(days ÷ 7)
    3. months = whole calendar months between the dates, plus the leftover days
    MATH
  • Aquarium Volume Calculator
    1. rectangular: litres = length × width × height (cm) ÷ 1000
    2. round: litres = π × (diameter ÷ 2)² × height (cm) ÷ 1000
    3. US gallons = litres ÷ 3.785411784
    MATH
  • Aquarium Water Change Calculator
    1. water to replace = tank volume × percentage ÷ 100
    MATH
  • Horse Weight Calculator
    1. weight (kg) = heart girth² × body length ÷ 11,900, with girth and length in cm (Carroll & Huntington 1988)
    CH88
  • Pet Food Bag Duration Calculator
    1. days = bag size (g) ÷ (daily grams per pet × number of pets)
    MATH
  • Cat Food Cost Calculator
    1. grams/day = MER ÷ (kcal per kg ÷ 1000)
    2. cost/day = grams/day ÷ 1000 × (bag price ÷ bag kg)
    3. month = day × 365/12
    4. year = day × 365
    NRC06MERCKMATH
  • Pet Meal Size Calculator
    1. grams per meal = daily grams ÷ meals per day
    2. kcal per meal = grams per meal × kcal per kg ÷ 1000
    MATH
  • Aquarium Water Weight Calculator
    1. water weight (kg) = tank volume (litres) × 1 kg per litre
    2. pounds = kg × 2.20462
    MATH
  • Pond Volume Calculator
    1. rectangular: L × W × D
    2. round: π × (diameter ÷ 2)² × D
    3. oval: π ÷ 4 × L × W × D (metres), × 1,000 = litres
    MATH
  • Dog Age from Birth Date Calculator
    1. age (years) = days since birth ÷ 365.25
    2. size chart: year 1 ≈ 15, year 2 ≈ 24, then +4 / +5 / +6 / +7 per year (small / medium / large / giant)
    3. epigenetic: 16 × ln(age) + 31 (Wang 2020)
    INDUSTRYWANG20
  • Cat Age from Birth Date Calculator
    1. age (years) = days since birth ÷ 365.25
    2. human years: year 1 = 15, year 2 = 24, then +4 per year
    3. life stages: kitten <1, young adult 1–6, mature 7–10, senior >10
    AAFP_LSAAFP_LS10
  • Dog Pregnancy Week Calculator
    1. day = today − mating date
    2. week = floor(day ÷ 7) + 1
    3. due ≈ 63 days from mating (normal range 58–68)
    MERCKCONC11
  • Cat Pregnancy Week Calculator
    1. day = today − mating date
    2. week = floor(day ÷ 7) + 1
    3. due ≈ 63–65 days from mating (normal window 61–69)
    MERCK
  • Pet Insurance Break-Even Calculator
    1. annual premium = 12 × monthly premium
    2. break-even vet bills per year = annual premium ÷ repay % + annual excess
    3. payout = (bill − excess) × repay %
    MATH
  • Pet Emergency Fund Calculator
    1. gap = target − already saved
    2. monthly = gap ÷ months, or months = ceiling(gap ÷ monthly amount)
    MATH
  • Pet Boarding Cost Calculator
    1. total = nights × nightly rate × number of pets + fixed fees
    MATH
  • Dog Walking Cost Calculator
    1. per week = walks per week × price per walk
    2. per month = per week × 52 ÷ 12
    3. per year = per week × 52
    MATH
  • Monthly Pet Budget Calculator
    1. monthly total = food + routine vet + insurance + grooming + treats and toys + other
    2. yearly total = monthly × 12
    MATH
  • Cat Food Cans per Day Calculator
    1. MER = 70 × BW(kg)^0.75 × life-stage factor
    2. cans per day = MER ÷ kcal per can
    NRC06MERCK
  • Dog Food Cans per Day Calculator
    1. MER = 70 × BW(kg)^0.75 × life-stage factor
    2. cans per day = MER ÷ kcal per can
    NRC06MERCK
  • Dog Wet and Dry Food Calculator
    1. MER = 70 × BW(kg)^0.75 × life-stage factor
    2. wet grams = MER × wet share ÷ (wet kcal per kg ÷ 1000)
    3. dry grams = MER × (1 − wet share) ÷ (dry kcal per kg ÷ 1000)
    NRC06MERCK
  • Pet Food Energy Converter
    1. kcal per g = value ÷ grams in the unit
    2. kcal per kg = kcal per g × 1,000
    3. per 100 g = × 100
    4. per lb = × 453.59237
    5. per oz = × 28.349523125
    MATH
  • Pet Weight Change Calculator
    1. total % = (current − start) ÷ start × 100
    2. per week % = total % ÷ weeks
    3. pace compared with AAHA's 1–2% of body weight per week
    AAHA_WMMATH
  • Pet Food Price per 1,000 kcal Calculator
    1. price per 1,000 kcal = bag price ÷ (bag kg × kcal per kg ÷ 1,000)
    MATH
  • Pet Birthday Calculator
    1. next birthday = the birth date's month and day in this or next year (29 Feb is celebrated on 28 Feb in non-leap years)
    2. days until = next birthday − today
    MATH
  • Pet Weight Converter
    1. 1 lb = 453.59237 g
    2. 1 oz = 28.349523125 g
    3. 1 kg = 1,000 g
    4. pounds and ounces = whole pounds plus the remaining ounces
    MATH
  • Pet Measurement Converter
    1. 1 inch = 2.54 cm exactly
    2. 1 foot = 12 inches
    3. millimetres = cm × 10
    MATH
  • Pet Temperature Converter
    1. °F = °C × 9 ÷ 5 + 32
    2. °C = (°F − 32) × 5 ÷ 9
    MATH
  • Cat Litter Cost Calculator
    1. cost per week = price per kg × kg used per week
    2. weeks per bag = bag kg ÷ kg per week
    3. month = week × 52 ÷ 12
    4. year = week × 52
    MATH
  • Pet Grooming Cost Calculator
    1. per year = sessions per year × price per session + 12 × monthly home supplies
    2. per month = per year ÷ 12
    MATH
  • Pet Annual Vet Cost Calculator
    1. yearly = check-ups × price + vaccines + 12 × monthly preventives + dental + other
    2. monthly = yearly ÷ 12
    MATH
  • Pet Food Cost per Meal Calculator
    1. price per kg = bag price ÷ bag kg
    2. cost per meal = price per kg × grams per meal ÷ 1000
    3. per day = per meal × meals per day
    MATH
  • Dog Overweight Percentage Calculator
    1. % over ideal = (current − ideal) ÷ ideal × 100
    2. about 10% over ideal per body condition score point above 5 (Laflamme 1997)
    LAFTWSAVA_N
  • Pet Vaccination Due Date Calculator
    1. due date = last date + interval in months (shortened to the last day of a shorter month)
    2. days until = due date − today
    MATH
  • Aquarium Substrate Volume Calculator
    1. litres = length × width × depth (cm) ÷ 1000
    2. US gallons = litres ÷ 3.785411784
    MATH
  • Aquarium Filter Turnover Calculator
    1. turnovers per hour = flow rate per hour ÷ tank volume
    2. minutes per full cycle = 60 ÷ turnovers per hour
    MATH
  • Pond Pump Turnover Calculator
    1. turnovers per hour = pump flow per hour ÷ pond volume
    2. minutes per full cycle = 60 ÷ turnovers per hour
    MATH
  • Pond Liner Size Calculator
    1. liner length = pond length + 2 × depth + 2 × overlap
    2. liner width = pond width + 2 × depth + 2 × overlap
    MATH
  • Pet Food Run-Out Date Calculator
    1. days = bag grams ÷ daily grams
    2. run-out date = start date + days
    3. reorder date = run-out date − lead days
    MATH
  • Pet Weight Goal Date Calculator
    1. weeks = ceiling(ln(target ÷ current) ÷ ln(1 − weekly loss))
    2. date = start date + weeks × 7
    3. weekly loss chosen from AAHA's 1–2% of body weight
    AAHA_WMMATH
  • Pet Treat Energy Converter
    1. kcal per treat = kcal per 100 g × treat weight in grams ÷ 100
    2. treats per pack = pack grams ÷ treat grams
    MATH
  • Dog vs Cat Cost Calculator
    1. lifetime = one-off costs + 12 × monthly cost × lifespan (years), for each pet
    2. default lifespans: dog 12.5 years (McMillan 2024), cat 11.7 years (Teng 2024)
    MATHMCM24TENG24
  • Pet Travel Food Calculator
    1. food to pack (g) = (trip days + spare days) × grams per day × pets
    2. kg = g ÷ 1000
    3. lb = g ÷ 453.59237
    MATH
  • Horse Hay Cost Calculator
    1. price per kg = bale price ÷ bale kg
    2. cost per day = price per kg × kg fed per horse per day × horses
    3. bale lasts = bale kg ÷ daily kg
    MATH
  • Pet Adoption vs Purchase Cost Calculator
    1. total for each option = price or fee + vet costs (vaccines, neutering, microchip) + supplies
    2. difference = option B − option A
    MATH
  • Horse Maintenance Nutrients Calculator
    1. values interpolated linearly between the NRC (2007) table rows at 200, 500 and 900 kg (e.g. 16.7 Mcal digestible energy and 630 g protein at 500 kg)
    MERCKHNRC07
  • Lactating Mare Nutrients Calculator
    1. values interpolated linearly between the NRC (2007) table rows at 200, 500 and 900 kg, shown as low–high ranges for the first 3 months and for 3 months to weaning
    MERCKHNRC07
  • Horse Hay Needs Calculator
    1. hay as fed (kg/day) = body weight × 1.5–2.5% ÷ hay dry matter %
    2. maximum intake 2.5–3.0% of body weight as dry matter
    ACESMERCKH
  • Dog Life Stage Calculator
    1. puppy to about 6–9 months
    2. young adult to about 3–4 years
    3. mature adult until the last 25% of the estimated lifespan
    4. senior = last 25% (AAHA 2019)
    AAHA_LS19MCM24

Sources

Primary and authoritative references used across the calculators.

  1. AAFP_LS
    AAFP/AAHA (2021) Feline Life Stage GuidelinesPrimary / guidelineUsed by 2 calculators: Cat Age Calculator, Cat Age from Birth Date Calculator
    ↗
  2. AAFP_LS10
    Vogt A.H. et al. (2010) AAFP-AAHA Feline Life Stage Guidelines. Journal of Feline Medicine and Surgery 12:43–54Primary / guidelineUsed by 2 calculators: Cat Age Calculator, Cat Age from Birth Date Calculator
    ↗
  3. NRC06
    NRC (2006) Nutrient Requirements of Dogs and Cats, National Academies PressPrimary / guidelineUsed by 14 calculators: Cat Food Calculator, Dog Calorie Calculator, Dog Food Calculator +11 more
    ↗
  4. WSAVA_N
    WSAVA Global Nutrition Guidelines (incl. 9-point BCS charts)Primary / guidelineUsed by 10 calculators: Cat Food Calculator, Dog Body Condition Score & Ideal Weight Calculator, Dog Food Calculator +7 more
    ↗
  5. MERCK
    Merck Veterinary Manual — Nutritional Requirements of Small Animals (incl. maintenance energy table)Primary / guidelineUsed by 17 calculators: Cat Food Calculator, Cat Pregnancy Due Date Calculator, Dog Calorie Calculator +14 more
    ↗
  6. MATH
    Pure arithmetic / unit conversion on user inputs (no external constant)ArithmeticUsed by 40 calculators: Cost of Owning a Dog Calculator, Dog Food Cost Calculator, Dog Food Cups to Grams Calculator +37 more
  7. MCM24
    McMillan K.M. et al. (2024) Longevity of companion dog breeds: those at risk from early death. Scientific ReportsPrimary / guidelineUsed by 3 calculators: Cost of Owning a Dog Calculator, Dog vs Cat Cost Calculator, Dog Life Stage Calculator
    ↗
  8. AAHA_LS
    AAHA (2019) Canine Life Stage GuidelinesPrimary / guidelineUsed by 1 calculator: Dog Age Calculator
    ↗
  9. WANG20
    Wang T. et al. (2020) Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome. Cell SystemsPrimary / guidelineUsed by 2 calculators: Dog Age Calculator, Dog Age from Birth Date Calculator
    ↗
  10. INDUSTRY
    Size-based human-year chart: commonly published rule of thumb (an approximation, not taken from the AAHA life-stage guidelines)Industry / practice guidanceUsed by 4 calculators: Dog Age Calculator, Dog Crate Size Calculator, Dog Harness Size Calculator +1 more
  11. LAF97
    Laflamme D. (1997) Development and validation of a body condition score system for dogs. Canine PracticePrimary / guidelineUsed by 1 calculator: Dog Body Condition Score & Ideal Weight Calculator
  12. AKC_G
    AKC / vet-practice owner guidance (practical rule of thumb)Primary / guidelineUsed by 1 calculator: Dog Crate Size Calculator
    ↗
  13. AAFCO
    AAFCO Dog & Cat Food Nutrient Profiles / label guidancePrimary / guidelineUsed by 2 calculators: Dog Food Calorie, Dry Matter Basis Calculator
    ↗
  14. AAHA_WM
    AAHA (2014) Weight Management Guidelines for Dogs and CatsPrimary / guidelineUsed by 5 calculators: Dog Treat Calorie Calculator, Dog Weight Loss Calculator, Cat Treat Calorie Calculator +2 more
    ↗
  15. PRACTICE
    Raw feeding portion convention (about 2–3% of ideal body weight; 80/10/10 ratio) — practitioner guidance, not a scientific standardIndustry / practice guidanceUsed by 1 calculator: Raw Dog Food Calculator
  16. TENG24
    Teng K.T. et al. (2024) Life tables of annual life expectancy and risk factors for mortality in cats in the UK. Journal of Feline Medicine and Surgery 26Primary / guidelineUsed by 2 calculators: Cost of Owning a Cat Calculator, Dog vs Cat Cost Calculator
    ↗
  17. CH88
    Carroll C.L. & Huntington P.J. (1988) Body condition scoring and weight estimation of horses. Equine Veterinary Journal 20:41–45Primary / guidelineUsed by 1 calculator: Horse Weight Calculator
    ↗
  18. CONC11
    Concannon P.W. (2011) Reproductive cycles of the domestic bitch. Animal Reproduction Science 124:200–210Primary / guidelineUsed by 1 calculator: Dog Pregnancy Week Calculator
    ↗
  19. LAFT
    Laflamme D. (1997) Development and validation of a body condition score system for dogs. Canine Practice 22:10–15Primary / guidelineUsed by 1 calculator: Dog Overweight Percentage Calculator
  20. MERCKH
    Merck/MSD Veterinary Manual — Estimated Average Minimum Daily Nutrient Requirements of Mature Horses and Ponies (table adapted from NRC 2007)Primary / guidelineUsed by 3 calculators: Horse Maintenance Nutrients Calculator, Lactating Mare Nutrients Calculator, Horse Hay Needs Calculator
    ↗
  21. NRC07
    NRC (2007) Nutrient Requirements of Horses, 6th ed., National Academies PressPrimary / guidelineUsed by 2 calculators: Horse Maintenance Nutrients Calculator, Lactating Mare Nutrients Calculator
    ↗
  22. ACES
    Alabama Cooperative Extension — Decreasing costs of feeding horses (forage intake of 1.5–2.5% of body weight as dry matter)Primary / guidelineUsed by 1 calculator: Horse Hay Needs Calculator
    ↗
  23. AAHA_LS19
    AAHA (2019) Canine Life Stage Guidelines. Journal of the American Animal Hospital Association 55:267–290Primary / guidelineUsed by 1 calculator: Dog Life Stage Calculator
    ↗