It will soon be payback time for Maryland students who have spent those lazy snow days sleeping until 10 a.m., playing with friends and sledding.

Twenty-two of Maryland's 24 school districts have already plowed through the days they build into their annual calendars for snow and bad-weather closings, according to an unofficial tally by state education officials made before this week's storm. State law requires students to go to school for 180 days.

   See updated closings for Thursday

So if the snow falls as predicted and schools close a day or two this week, local superintendents will have to start adding days.

Already, seven school districts will be open on Monday, canceling plans to take off the Presidents Day holiday, and it is likely that many school districts will have to add days to the end of the school year or take away part of spring vacation.

Here's how bad it is in Garrett County in Western Maryland this year. Garrett is in the mountains and not new to snow, so it allots six days a year for bad weather. As of Wednesday, the schools have been closed 14 days. One day, schools closed for cold because of a wind chill of minus 30 degrees.

Baltimore City and Anne Arundel, Howard, Carroll and Harford counties have all used up the days set aside for bad weather.

Of the Baltimore-area counties, only Baltimore County has a day left in the bank. It announced Wednesday night that schools would be closed Thursday, which means the school system has used six of its seven allotted days.

Once the winter of 2014 is truly over and there's no chance of a school's closing because of bad weather, school districts can ask the Maryland State Board of Education to give them a waiver to the law.

State superintendents can extend waivers when the governor declares a state of emergency, which Gov. Martin O'Malley did ahead of Thursday's expected snow.

But those waivers have been granted only rarely in the past.

The former state school superintendent, Nancy S. Grasmick, gave statewide waivers to schools only when hurricanes and blizzards forced schools to close for extended periods of time. In 1996 after a snowy winter, a divided school board reluctantly granted the waiver to every district. And after a major snowstorm in 2003, the board gave Grasmick the authority to hand out waivers, but she did not allow all school districts to use them. In 2010, when record snowstorms kept students home for as many as 10 days, she gave waivers for up to five days.

School calendars vary across the state, so the state cannot adjust calendars uniformly.

Baltimore City schools have used the five inclement-weather days built into their calendar, and officials said the district would look to convert professional development days into school days or adjust the last day of the school year.

Howard County has used up its five days and will consider asking for a waiver, said a school spokeswoman, Rebecca Amani-Dove.

"We haven't made any decisions yet," she said. "Nothing is off the table at this point."

Carroll County also built five days into its calendar and has used eight, including Thursday. The district has already scheduled a make-up day on Feb.18, which was originally a professional development day. The district also will seek a waiver, according to a spokeswoman. If the waiver is not granted, the county will extend the school year.

Harford County public schools have used their seven snow days and will ask for a waiver from the state, according to a spokesperson.

Baltimore County superintendent Dallas Dance will consider all options, including asking for a waiver, if the county uses all its snow days, according to Mychael Dickerson, a spokesman.

Dance is concerned that high school students get enough time in their classrooms. The county high school days are shorter than those of most high schools in the state.