Denunciation Period

A denunciation period is the waiting interval a treaty imposes between the moment a state party formally notifies its intent to withdraw (the act of denunciation) and the moment that withdrawal becomes legally effective. During this window, the state generally remains bound by all treaty obligations, including dispute settlement clauses, reporting duties, and substantive commitments.

The default rule under customary law, codified in Article 56 of the Vienna Convention on the Law of Treaties (1969), is that where a treaty contains no withdrawal clause, a party must give at least twelve months' notice of its intention to denounce, and only if denunciation is implied by the nature of the treaty or the intent of the parties. Many treaties, however, set their own period:

• The UN Charter contains no denunciation clause at all.
• The Rome Statute of the ICC (Article 127) requires one year notice; obligations accrued before effective withdrawal survive.
• The WHO Constitution historically required one year notice plus payment of dues.
• The Paris Agreement (Article 28) allowed denunciation only three years after entry into force, with a further one-year notice — a structure that shaped the United States' 2019 notice and 4 November 2020 effective withdrawal.
• ICSID Convention (Article 71) sets six months, as invoked by Bolivia (2007), Ecuador (2009), and Venezuela (2012).
• Bilateral investment treaties commonly include "survival" or sunset clauses extending protections for 10–20 years after termination.

The denunciation period serves several functions: it gives counterparties time to adjust expectations, preserves accrued rights and pending procedures, and discourages impulsive exit. It can also be litigated — for instance, the timing of the United Kingdom's Article 50 TEU notice (29 March 2017) triggered a two-year negotiation window that was extended by mutual agreement before Brexit took effect on 31 January 2020.