The PDSA and RSPCA both moved away from "multiply by 7" years ago

UK animal welfare charities including the PDSA and RSPCA have long stopped recommending the simple "1 dog year = 7 human years" rule in their public guidance, since it dramatically understates how fast a young dog matures and overstates the aging of an older dog. This calculator's non-linear approach, weighted by breed size, reflects the same general shape used in their current owner guidance.

UK pet insurers price by exactly this kind of age curve

Several UK pet insurance providers set premiums using breed-size-adjusted age curves similar to the one this calculator uses, which is part of why a large-breed dog's insurance often rises more steeply from around age 6-7 onward than a small breed's does at the same calendar age, reflecting the faster biological aging large breeds experience.