A thumb mounted ammunition loader engages a digit, preferably a thumb, of the user's hand to protect the digit while loading ammunition into a magazine. The thumb mounted ammunition loader additionally maintains traction to the pressure applied to the ammunition, as the thumb mounted ammunition loader provides a barrier to depositing skin oil onto the ammunition. The thumb mounted ammunition loader includes a digit-mounting tube, a digit-receiving opening, a distal-closed end, and at least one joint-accommodating aperture. The digit-mounting tube engages the digit. The digit-receiving opening allows the digit to be inserted into the digit-mounting tube. The distal-closed end interfaces with the ammunition as the user applies pressure to the ammunition through the distal-closed end. The at least one joint-accommodating aperture provides flexibility of the thumb mounted ammunition loader for the user to maintain range of motion of the digit.