The two Nordic currencies sharply underperformed in 2017 amid worries that house prices could collapse, despite predictions at the start of last year of Nordic currency strength.

The outlook for 2018 is nevertheless more positive, and the central banks of Norway and Sweden plan to begin a gradual tightening of monetary policy after years of ultra-cheap cash, which may also contribute to currency strength.

While Sweden's Riksbank has so far signalled a rate hike in the first quarter of 2019, it may move this to the last quarter of 2018, SEB's chief foreign exchange strategist Carl Hammer said.

"We expect a high March inflation (figure) and that will be the first trigger for a stronger (Swedish) crown," he said, while cautioning the currency's upside potential would be limited as long as the central bank keeps a negative repo rate.

For oil-producer Norway, a partial recovery in the price of crude is expected to spur faster growth, and the central bank now predicts a rate hike by autumn, against an earlier view of a December tightening.

The more hawkish Norwegian stance has strengthened its currency against the Swedish crown by some 8 percent since the start of 2018, although the Reuters poll suggested this gap would be partially reversed in the coming year.

Overall, economists predicted the Swedish crown will gain 10 percent from current levels against the dollar and 6.5 percent against the euro by the same time next year.

The Norwegian crown was meanwhile set to rise by 7.4 percent against the dollar and 4 percent against the euro over the next 12 months.

"The Norwegian crown is unreasonably undervalued, when you consider the outlook for the Norwegian economy and rising interest rates," DNB Chief Economist Kjersti Haugland said.

"In the last year we have seen a lot of misery priced into the Norwegian currency, and the level is now weaker than fundamental factors indicate. That is the main reason why we expect a stronger crown," Haugland added.