Before there were computers, insurance companies used a round slide rule device called an "Insurance Wheel" to calculate how much premium was to be refunded for a policy cancelled before its expiration date.

Insurance Wheel replaces the old circular slide rules. Insurance Wheel is a useful tool for insurance brokers as well as insurance carriers.

The Insurance Wheel calculator supports the 3 normal ways of calculating how much premium is returned when an insurance policy is cancelled before its expiration date:

Pro Rata - simple fraction of unearned policy period
Short Rate (90% pro rata) - pro rata discounted 10%
Short Rate - table driven