And the reduced expected lifespan for an outdoor cat is a statistical average based on the increased likelihood of getting run over by a vehicle, or in a fight with wildlife or another cat and getting an infection (the latter chance reduced by neutering and vaccinations) - a cat that has lived outdoors but had made it to old age without contracting FIV or FeLV and is now indoors will have the same ongoing life expectancy as a cat that has always been indoors.