Western governments have focused on calculating when Iran's foreign exchange reserves will run low because they want to force the government to yield on nuclear development before it can enrich enough uranium and acquire sufficient knowledge to build a working warhead. Israel's government believes that date could come late next spring; the Obama administration believes it may be several years off.
Other Western governments have avoided saying publicly when they think Iran will reach the crisis point.
Mark Dubowitz, executive director of the Foundation for Defense of Democracies, a Washington think tank that has pressed for tougher sanctions, said an economic meltdown would need to occur at least six months before Iran reaches the nuclear threshold. That would allow time for the economic shock to "cascade through the political system, and convince the leadership they need to change course... These guys are hard core revolutionaries," said Dubowitz.
Cliff Kupchan, a former State Department official at the Eurasia Group consulting firm, said he believes it's impossible to estimate when Iran's economy will be disabled because so many complex factors are involved. Estimates of Iran's accessible foreign exchange reserves vary wildly, from $30 billion to $110 billion, he noted.
"The numbers available to me don't allow a prediction," he said.