Since the NPT entered into force in 1970, three states that were not parties to the Treaty have conducted nuclear tests, namely India, Pakistan, and North Korea. North Korea had been a party to the NPT but withdrew in 2003.
Israel is also generally understood to have nuclear weapons, but does not acknowledge it (Israel maintains a policy of deliberate ambiguity), and is not known definitively to have conducted a nuclear test. Israel is estimated to possess somewhere between 75 and 400 nuclear warheads. One possible motivation for nuclear ambiguity is deterrence with minimum political cost.
States that formerly possessed nuclear weapons are South Africa (developed nuclear weapons but then disassembled its arsenal before joining the NPT) and the former Soviet republics Belarus, Kazakhstan, and Ukraine.
According to Bulletin of the Atomic Scientists Nuclear Notebook, the total number of nuclear weapons worldwide is estimated at 9,220 in 2017.
The following is a list of states that have admitted the possession of nuclear weapons or are presumed to possess them, the approximate number of warheads under their control, and the year they tested their first weapon and their force configuration. This list is informally known in global politics as the "Nuclear Club". With the exception of Russia and the United States (which have subjected their nuclear forces to independent verification under various treaties) these figures are estimates, in some cases quite unreliable estimates. In particular, under the Strategic Offensive Reductions Treaty thousands of Russian and U.S. nuclear warheads are inactive in stockpiles awaiting processing. The fissile material contained in the warheads can then be recycled for use in nuclear reactors.