A self-retracting knife includes a housing having a forward end defining a blade aperture, and a blade carrier supports a removable knife blade and is movable within the housing from a fully extended position with the blade projecting from the blade aperture and a fully retracted position by a tension spring. An anti-retraction latch member is supported by the housing and is movable with finger pressure to a position that stops the blade carrier from fully retracting so that the knife blade is partially extended through the blade aperture. In other embodiments, the blade carrier extends through a carrier aperture at the opposite end of the housing for extending the blade carrier, and an adjustable extension limiter also extends through the carrier aperture for limiting forward movement of the blade carrier and projection of the blade through the blade aperture.