"I haven't ruled it out for the rest of the parliament", the Scottish National party leader said.
The hour-long debate between six Scottish leaders, broadcast on BBC One in Scotland, also saw Ms Sturgeon say she wanted head teachers to have more control over how education budgets are spent, although she did not go as far as saying schools should be taken out of local authority control.
Scottish Labour's Kezia Dugdale said she would set new thresholds so "those earning less than £20,000 wouldn't pay any more tax", the rise would begin for those earning £21,000.
She said she would ask her council of economic advisers to examine each year to see if there were ways of mitigating the risk of wealthy Scots moving their money rather than pay a 50p rate.
If Scotland had voted Yes instead of No in September 2014, today would have been marked in the diary as the first day of independence.
The Scottish government will use its new powers to stop the planned increase in the level at which households in Scotland start paying the top rate of income tax, First Minister Nicola Sturgeon said.
Under Labour's replacement for the council tax, households would pay a percentage of what their property is worth, but the maximum charge would be capped at £3,000.
Kezia Dugdale with Labour candidate James Kelly
An SNP spokesperson said the IFS projections showed Scotland's fiscal balance would improve each year between now and the end of the decade and growth in tax revenues for the country's non-oil economy would offset offshore losses.
Labour and the Lib Dems insist Holyrood's existing but limited powers could be used to immediately add 1p to the basic rate of income tax in Scotland, to fund about £500m in extra public spending - a policy rejected by the SNP. The reason for that is I have got independent civil service analysis saying it might lose us £30 million.
Scottish Conservative leader Ruth Davidson said: "Let's be clear, it wouldn't be the rich who'd suffer from the SNP's con trick on independence".
The Scottish Government had earmarked March 24 as "independence day" if voters in the 2014 referendum had supported leaving the UK. Low earners would slowly see the personal allowance to £12,750 by 2021, £250 more than George Osborne, the chancellor, plans for the rest of the UK.
He said: "She was for it on Monday, against it on Tuesday and tonight she's not quite sure".
With the SNP expected to romp home on 5 May and Labour and the Conservatives nearly neck-and-neck in the race for second place, both Ms Dugdale and Ms Davidson attempted to position themselves as leader of the official opposition.
Patrick Harvie, the Scottish Green party leader who is hoping to take leftwing pro-independence votes from the SNP, was equally critical of the SNP's refusal to increase taxes on wealth and income.
Biyombo's double-double lifts Raptors over Magic
Victor Oladipo and Evan Fournier had 21 points apiece for the Magic. "They made big plays down the stretch", Vogel said. The Magic (29-40) will continue their east coast road trip with a visit to Boston tomorrow.