LONDON- U.S. investment bank JPMorgan expects the S&P500 index to surge to 3,900 points if U.S. President Donald Trump is re-elected next week, calling such an outcome the most favourable for stock markets.

A rise to 3,900 would mark a 12.6% jump from Friday's closing level.

A clean sweep by Democrats would be "mostly neutral" for markets, JPM said in a note received on Monday, adding: "We see an 'orderly' Trump victory as the most favourable outcome for equities."

The odds of a "blue wave" have narrowed slightly since mid-October. Former vice president Joe Biden has a substantial lead in national opinion polls, although the contest is closer in battleground states likely to decide the race. 

JPMorgan said several of its data gatherings, such as voter registration, Twitter sentiment, point to a "tightening race". The bank sees a gridlock in the election as a "net positive" for stocks.

Within sectors, JPM sees beaten down energy and financial stocks to likely be key beneficiaries of a Trump victory, while a Biden win could trigger a rotation from U.S. growth stocks to non U.S. growth stocks, given the risk of higher taxes.

"We find that energy, financials and healthcare sectors could likely see the most outsized moves as they have been explicitly referenced by each candidate on the campaign trail," the bank added.

(Reporting by Thyagaraju Adinarayan; Editing by Sujata Rao and Alison Williams) ((thyagaraju.adinarayan@tr.com; +44 20 7542 7015; Reuters Messaging: thyagaraju.adinarayan.thomsonreuters.com@reuters.net; Twitter @thyagu))