A flat salary cap is forcing the Buffalo Bills to create more room under the NFL salary cap before the free-agent spending season begins March 12.

The Bills’ release Monday of George Wilson and Nick Barnett left them $20.9 million under the projected salary cap for this season, according to News figures.

However, a lot of that space is going to be eaten up by other expenses before they start pursuing players from other teams.

The Bills need about $5.5 million in cap space for their 2013 draft choices. They need $6.8 million for a franchise tag to retain the rights to safety Jairus Byrd. A tender offer for restricted free agent David Nelson is $1.3 million.

Those costs total $13.6 million.

How much space do the Bills need to do their free-agent shopping? Two top-flight starters would cost about $7 million or $8 million in cap space.

Last year they signed Stevie Johnson, their top receiver, to a $36 million deal, and he counted $4.3 million against their cap. They signed Mark Anderson to a $19 million deal. He cost $3.5 million against the cap in his first season in Buffalo.

So it’s a relatively tight cap situation, which could make it tricky to fit a new deal for guard Andy Levitre into the Bills’ financial plan for this year.

The release of Barnett saved $3.5 million in cap space. The release of Wilson saved $2.925 million in space.

The Bills will need to lower the cost of some more veterans if they want to make some significant free-agent additions.

The No. 1 prospect on the savings list is quarterback Ryan Fitzpatrick, who is scheduled to cost $10.45 million against the cap. That includes a base salary of $4.5 million and a $3 million roster bonus due in March. If Fitzpatrick is released before the roster bonus is paid, he will count $10 million against the Bills’ salary cap in 2013, due to amortized bonus money already paid that would roll into the Bills’ cap accounting. The way to reduce the cap hit is to get him to agree to a pay cut.

Defensive end Chris Kelsay is another prospect. He has the third highest cap figure on the Bills’ roster, behind defensive end Mario Williams and Fitzpatrick. Kelsay is due to count $5.97 million against the cap, and the Bills would save $4.9 million if he were released. Kelsay played 50 percent of the defensive snaps last year before he was lost for the season to injury.

The NFL’s projected salary cap for this year is $121 million per team. That’s up less than $1 million from last season.

Each team is allowed to roll over unused cap space from last year, if it so chooses. The Bills rolled over $9.8 million in unused space, so their actual cap limit is $130.4 million. The Bills’ total cap cost as of this week was about $116 million, according to News calculations.

The Bills’ top 12 cap figures: Mario Williams ($12.4 million), Fitzpatrick ($10.45 million), Kelsay ($5.975 million), Kyle Williams ($5.95 million), Stevie Johnson ($5.67 million), Marcell Dareus ($5.56 million), C.J. Spiller ($5.04 million), Terrence McGee ($4.6 million), Mark Anderson ($4 million), Brad Smith ($3.75 million), Fred Jackson ($3.7 million) and Eric Wood ($3.34 million).

The Bills had a lot more cash space last year. They entered the free agency season a year ago with about $20 million in cap space.

The Bills are coming off two straight years of big spending.

In terms of actual cash paid out, the Bills spent $139 million in 2012, according to News totals. That was the third highest spending total in the NFL, according to ESPN’s John Clayton. The total was $5 million over their adjusted cap and $18.5 million over the base NFL cap limit. In 2011, the Bills spent $137.4 million, which was $15 million over the NFL’s base cap level. The 2011 cash spend total ranked Buffalo about 16th in the NFL.