Sales of the new iPhone could add between a quarter and a half of a percentage point to the annualized rate of economic growth in the fourth quarter, J.P. Morgan Chase & Co.'s chief U.S. economist Michael Feroli estimates. That could help cushion the sluggish U.S. economy from other risks in the final months of the year.

That could help cushion the sluggish U.S. economy from other risks in the final months of the year.

In a note to clients Monday, titled "Can one little phone impact GDP?," Mr. Feroli walks through the math: J.P. Morgan's equity analysts expect Apple to sell about eight million new iPhone units in the final three months of 2012.

If the phone sells for around $600, with about $200 of it counted as imported components, then $400 per phone would add to the government's measure of gross domestic product, the total value of the economy's output.

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