It's only been five years since Americans hit a grand total of $3 trillion in consumer debt and yet, by the end of 2018, that figure is expected to jump by another trillion.

In the first nine months of 2018, Americans had a cumulative $3.93 trillion in debt, excluding mortgages, with $1 trillion of that from credit cards and $2.93 trillion from other sources such as student loans and auto loans. With holiday shopping underway, Americans' credit card bills are set to increase by at least 5 percent, according to mortgage site LendingTree. That $600 million or so in extra spending is likely to bring consumer debt to a new high of $4 trillion.

Still, LendingTree's chief economist Tendayi Kapfidze says consumers shouldn't worry. "It's a big number, but it's actually not that concerning, because of the income growth we've seen since the crisis," Kapfidze tells CNBC Make It.

One reason he's not too worried, Kapfidze says, is that the economy is more stable in 2018 than it was in 2008, and real estate values and consumer bank deposits have grown more than debt has. "Deposits have grown by $2.5 trillion more than consumer debt, and homeowners have nearly $10 trillion more in home equity than they did a decade ago," he says.

Also, incomes have been growing at a faster rate than debt, he points out: "The net indebtedness of [individual] consumers is actually declining even though the total balance of debt is increasing."