(NBC) – Changes have been made that could have a profound impact on whether you can get a loan to buy a house, car or another big-ticket item.

Suffice it to say your FICO credit score is one of the most important numbers in your financial life.

“This is used in about 90% of lending decisions,” said Ted Rossman with CreditCards.com. “It’s going to determine whether or not you get that loan or line of credit in the first place. And, if you do, the interest rate you’ll pay.”

But now, the way your FICO score is determined has changed to what they call trended data.

If it’s just one month out of 12 where your spending is well above normal, then it’s not going to hurt your credit rating. But, if you fall behind paying your bills 3 or 4 months in row, get ready to pay more.

“Your debt’s creeping up, you’re starting to fall behind your bills…trended data is going to penalize somebody like that,” Rossman said. “I mean even on a $200,000 mortgage, we could be talking a difference of $25,000 over 30 years.”

He says the best way to avoid a hit from the changes: pay your bills on-time.