The “7 years” rule is a myth — pets age fast early, then slow. A better model gives the first two years extra weight, then a steady per-year rate — and dogs scale by size.
The example
5-year-old dog, +4/yr after 2.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | 21 + 3×4 | — |
| 3 | Human age | → ~33 |
The formula
The formula:
How it works
How it works:
- The first two years count about 10.5 human years each (~21 by age 2).
- After that, add a per-year rate — ~4–5 for small dogs, more for giant breeds.
- A plain ×7 overstates youth and understates old age — the IF model is closer.
- Pick the per-year rate by size with a lookup for breed-aware estimates.
Size flips the aging curve for dogs. Small breeds mature fast but live long; giant breeds are “seniors” by 6–7. A single ×7 multiplier can’t capture that, but a per-year rate chosen by weight class can — look it up from a small table and the same formula serves a Chihuahua and a Great Dane. (Cats roughly follow the small-dog curve.) This is a friendly estimate, not a clinical aging assessment.
Try it: interactive demo
Pet years and per-year rate after age 2.
Variations
Naive ×7 (for contrast)
The old rule:
Per-year rate by size
Breed-aware:
Cat estimate
Similar curve:
Pitfalls & errors
Not ×7. Aging is front-loaded then steady — use the IF model.
Size matters. Bigger dogs age faster — vary the per-year rate.
Estimate only. A friendly figure, not a health assessment.
Practice workbook
Frequently asked questions
How do I calculate pet age in human years in Excel?
Is the ×7 rule accurate?
How do I account for dog size?
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