It's a little misleading to hold Obama (or any other president) accountable for the deficit incurred during his first year of office. That's because the previous administration already set the federal budget for that fiscal year.
Before Obama took office, President Bush's last budget (FY 2009) created a deficit of $1.16 trillion. That fiscal year began on October 1, 2008, and continued until September 30, 2009. That means most of that deficit occurred after Obama took office in January. But since it wasn't his budget, it's not accurate to attribute it to him.
As a result of that method, As a result, Obama added $7.917 trillion to the debt.
Then there's this. Is it fair to blame any president for events over which he had no control? During Obama's terms, there was less federal income than usual. The recession and the Bush tax cuts reduced tax receipts. At the same time, the cost of Social Security, Medicare, and other mandatory programs continued to increase. The War on Terror, although technically over, was still being fought in Afghanistan and Iraq.
The fairest method is to measure the debt incurred by Obama's specific policies. The Congressional Budget Office does this for every program. The CBO found that Obama's largest contribution to the debt was the Obama tax cuts, which were an extension of the Bush tax cuts.
They added $858 billion to the debt in 2011 and 2012.
The next largest was the American Recovery and Reinvestment Act. It added $787 billion between 2009 and 2012. It cut taxes, extended unemployment benefits, and funded job-creating public works projects. Like the tax cuts, the ARRA stimulated the economy after the 2008 financial crisis
Obama increased military spending to around $800 billion a year. In fact, his security budget request of $895 billion in FY 2011 set a new record. In FY 2013, he requested $851 billion. That happened even though he withdrew troops from Iraq in 2012 and eliminated the threat from Osama bin Laden in 2011. Obama spent $857 billion in contingency funds during his administration. That was more than the $850 billion Bush devoted to the War on Terror.
What about the Patient Protection and Affordable Care Act? It didn't add anything to the debt in Obama's first term. Most of Obamacare's costs began in 2014 when the health insurance exchanges opened. It also extended coverage to more low-income people that year. But Obamacare's tax increases offset its costs to the tune of $104 billion between 2010 and 2019.
Congress and Obama also negotiated the sequestration budget cuts. That cut the deficit by a small percent. When all these are added up, Obama's debt contribution was $983 billion between 2009 and 2017.