Every property and casualty policy asks the buyer to choose a deductible, and the premium moves in the opposite direction. The relationship reflects which claims the insurer is being asked to handle.
Small claims dominate frequency, large claims dominate severity
Most claims filed against a typical policy are small. Large losses are rare, but each one costs far more than many small ones combined.
A deductible removes the small claims from the insurer's obligation entirely, since a loss below the threshold is never presented.
The insurer is therefore left covering fewer events, and the events it does cover are the ones it is structurally designed to absorb.
Administrative cost is largely per claim
Handling a claim requires intake, investigation, adjustment and payment, and much of that effort is similar regardless of the amount involved.
On a small loss, the handling cost can approach a meaningful share of the payment itself, which makes those claims inefficient to insure.
Removing them through a deductible cuts the insurer's expense base disproportionately, and competition passes part of that saving into the premium.
Deductibles also change policyholder behaviour
A policyholder with money at stake in every loss has an incentive to prevent losses and to absorb minor ones rather than claiming.
That reduces both the number of claims and the tendency for small losses to be presented at inflated values.
Insurers price for this expected behaviour change, which is part of why the premium reduction exceeds the pure arithmetic of the removed layer.
The saving is compared against a first-loss exposure
Choosing a higher deductible converts a certain annual saving into an uncertain occasional cost, which is a straightforward trade of variance for expected value.
The premium reduction is received every year whether or not a claim occurs, while the deductible is paid only when one does.
The choice therefore depends on how many claim events are expected over a long horizon and on whether the household holds enough cash to absorb one comfortably.
Percentage deductibles behave differently
Some perils, particularly wind, hail and earthquake, use a deductible expressed as a share of the insured value rather than a fixed sum.
The retained amount then scales with the property value and can be far larger than the flat deductible applied to other causes of loss.
Because these apply to exactly the events most likely to cause a large claim, they are the term most worth reading before assuming the stated deductible governs.