Why small changes in the Italian bond market have such big effects

In August, when the European Central Bank began buying Spanish and Italian government bonds , the two nations’ 10-year bond yields fell to 5% from 6.4%. What happens when the Bank stops buying? Some simple calculations from Leeds on Finance tell us why a small change in Italian yields has such significant effects on all of Europe:

You don’t need to know anything about economics to do some basic math. Here it is…lets imagine a country with debt-to-GDP of 120%. Lets also imagine that the country pays interest of 6% (that’s what Italy is currently paying; Greece is paying much more). If that’s the case, you’re paying interest that is equivalent to 7.2% of GDP. (That’s 120% x 6%.) Italy’s tax revenue is around 22% of GDP. If one-third of their tax revenue is needed to pay interest, the numbers don’t work out.

The US is different from Italy only in that our debt is a little lower, and our interest rates are a lot lower. But as soon as the markets figure out that we cannot or will not reduce our spending, then our situation looks very much like Italy's. What happens when we have to pay 1/3 of our federal budget to bondholders?

 So what are the long run prospects for Italy?

At a press conference after the first summit, Angela Merkel and Nicolas Sarkozy were asked whether they were reassured by Mr Berlusconi’s promises. The German and French leaders hesitated, stole a glance and smirked. The room burst into laughter. Rarely has a leader—from a founding member of the European Union, no less—been treated so disdainfully by his peers.