Every PetSums calculator works from a published figure or a standard formula. The figures live in one data file with the source beside each one, and the sums are covered by automated tests. Figures were last checked on 25 October 2026.
Dates
Due dates and season dates count whole calendar days from the date you enter, in UK date order. Leap years are handled. Dates are shown as, for example, 3 December 2026.
Rounding
Results are rounded for display only: grams and litres to the nearest whole number, kilograms of forage to one decimal place, and muzzle energy to two. The sums underneath use full precision.
Tool by tool
- Dog pregnancy: mating date + 63 days, window 56 to 72 days (PDSA).
- Dog season: last season + 182 to 213 days (6 to 7 months), or the dog's own gap if two dates are given (PDSA).
- Dog food: 70 × weight0.75 × a life stage factor, divided by the food's kcal per 100g (AAHA 2021).
- Pet insurance: 12 premiums plus excess and co-payment on each claim, against the full vet bills.
- Lambing: tup in + 143 to 147 days, typically 145 (NADIS, NSA).
- Calving: service date + breed gestation (ICBF).
- Horse weight: girth² × length ÷ 330 in inches gives pounds (Blue Cross, Kentucky Equine Research); forage 2 to 2.5% of bodyweight (BHS).
- Pond volume: length × width × depth × 1,000 litres; liner + 2 × depth + 1m (Hozelock); pump turnover from Pondkeeper.
- Air rifle muzzle energy: ½mv² with exact unit conversions, against the 1969 Rules limits.
- Drone registration: the weight and camera table in the CAA Drone Code (March 2026).
All sources
- PDSA: Pregnancy in dogs
- PDSA: Whelping, a guide to your dog giving birth (PDF)
- PDSA: Seasons in dogs
- AAHA 2021 Nutrition and Weight Management Guidelines: weight reduction in the obese pet
- ABI: Insurance payouts for pets top £1 billion for third year in a row (2024 figures)
- ABI: Guide to pet insurance
- NADIS: Lambing, the basics
- National Sheep Association: The sheep farming year
- Farm Advisory Service (Scotland): Raddle and keel marks
- ICBF: Gestation length in cattle
- Blue Cross: How to weigh your horse
- Kentucky Equine Research: Weight calculation
- PDSA: How to treat your dog
- British Horse Society: Feeding horses
- Hozelock: Building and designing your own garden pond
- Pondkeeper: How to choose the right pond pump
- legislation.gov.uk: Firearms (Dangerous Air Weapons) Rules 1969, rule 2 (PDF)
- legislation.gov.uk: Air Weapons and Licensing (Scotland) Act 2015, explanatory notes to Part 1
- CAA: The Drone and Model Aircraft Code (March 2026, PDF)
- CAA: Get an Operator ID
- CAA: New drone rules from 1 January 2026
When figures change
We recheck figures when a source publishes an update, and at least once a year. Changes are listed in the corrections log in our editorial policy.