WASHINGTON — To see where the presidential candidates stand on taxing the rich, just look at how they’d tax themselves. Under his own proposal, Mitt Romney would pay half what he would under President Barack Obama’s tax plan. For a man of Romney’s means, that could save almost $5 million a year.

For Obama, not as loaded as Romney but still well-off, losing re-election could provide a tax windfall. He’d save as much as $90,000 a year if Romney’s plan were enacted rather than his own tax-the-rich vision.

Two nonprofit research groups, the liberal-leaning Citizens for Tax Justice and conservative-leaning Tax Foundation, did the calculations, based on the most recent completed tax returns released by the candidates. Compared with what they owed in April, both men would be dinged in 2013 under Obama’s proposal, along with other wealthy taxpayers. They could expect savings under Romney, depending on which tax breaks the former Massachusetts governor decides to oppose.

Whether they go up or down, the candidates’ personal tax bills won’t make a dent in the nation’s trillion-dollar annual deficits, of course. But they illustrate a sticking point in the struggle to fix the nation’s finances: Just how much should affluent Americans pony up?

Democrats generally say the rich aren’t paying their fair share; most Republicans argue that raising taxes on the wealthy would slow investment that creates jobs. The dispute makes it tougher to tackle urgent budget issues, such as whether to extend the Bush-era tax cuts again before they expire Jan 1.