The old "multiply by seven" rule for dog years never held up — it treats a Chihuahua and a Great Dane as if they age identically, which they don't. This site was built to give a better estimate: one that accounts for species, and for dogs, adult size, since breed size changes the aging curve more than almost anything else.
The Windows 95-styled look is a deliberate throwback — partly because it's fun, and partly because a straightforward little desktop-app calculator felt like the right amount of seriousness for a tool like this. It's not a substitute for veterinary advice, just a more honest estimate than a rule of thumb from decades ago.
Dogs and cats age fastest in their first two years, then settle into a steadier pace. For dogs, how fast that later pace is depends heavily on adult size — small breeds tend to plateau for years, while large and giant breeds enter their senior years noticeably earlier. The breed size guide and the biology behind it go into more detail.
Found a bug, have a breed that's missing, or just want to say hi? Reach out at hello@aquaos.pet.