Owners are usually quoted a monthly premium and a percentage. Neither number is what the policy costs you over an animal’s life.

The excess is per condition, per year

A 100 excess is not paid once. It is paid on each new condition, and again on the same condition in a new policy year. A dog with a skin condition and an ear condition running across two policy years pays it four times.

That is why a claim below the excess is paid at nothing at all, and why small, frequent claims are the ones insurance is worst at.

Premiums are banded by age

The premium quoted for a three year old dog is not the premium you pay at eleven. Insurers band by age, and the increase compounds. Modelling the same policy across a whole life, rather than a single year, changes which side of the comparison wins.

The calculator on this site runs both lifetimes side by side: escalating premiums plus excess plus co-insurance against paying every claim in full. It does not tell you which to choose, because that depends on the numbers you type in.

What the model cannot see

It prices claims as a deterministic annual average. It cannot see variance, and variance is the single catastrophic claim insurance exists for. Read the output as a picture of the ordinary years, not as a reason to go uninsured.