when does a patent become enforceable
US patents with a filing date before June 8, 1995 provide protection for up to seventeen years counting from the date of grant (the date given with reference numeral 45), or 20 years from the filing date, whichever expires later. However, the patent holder is required to pay maintenance fees to keep his patent valid. In most European countries, these fees are yearly. The USA requires maintenance fees to be paid at 3.5 years, 7.5 years, and 11.5 years after issuance. If the holder does not pay a maintenance fee, the patent becomes abandoned.