QuickLinks -- Click here to rapidly navigate through this document

Exhibit 12.1


RATIO OF EARNINGS TO FIXED CHARGES
COGENT COMMUNICATIONS GROUP
(000's)

RATIO OF EARNINGS TO FIXED CHARGES
  YEAR
ENDED
12/31/2001

  YEAR
ENDED
12/31/2002

  YEAR
ENDED
12/31/2003

  YEAR
ENDED
12/31/2004

  YEAR
ENDED
12/31/2005

  NINE MONTHS
ENDED
9/30/2006

 
FIXED CHARGES                                      
Interest expense—net of capitalized interest   $ 7,945   $ 36,284   $ 19,776   $ 13,002   $ 11,747   $ 8,005  
Interest capitalized     4,400     800     100              
Estimated interest in rental expense     268     207     475     759     1,095     1,008  
   
 
 
 
 
 
 
Fixed charges   $ 12,613   $ 37,291   $ 20,351   $ 13,761   $ 12,842   $ 9,013  
   
 
 
 
 
 
 
EARNINGS                                      
Pretax income (loss)   $ (66,913 ) $ (91,843 ) $ 140,743   $ (89,660 ) $ (67,518 ) $ (43,786 )
Plus: Fixed Charges     12,613     37,291     20,351     13,761     12,842     9,013  
Less: Capitalized interest     (4,400 )   (800 )   (100 )            
Plus: Amortization of capitalized interest     291     786     858     888     885     664  
   
 
 
 
 
 
 
Earnings   $ (58,409 ) $ (54,566 ) $ 161,852   $ (75,011 ) $ (53,791 ) $ (34,109 )
   
 
 
 
 
 
 
Ratio of Earnings to Fixed Charges                 8.0                    
               
                   
Dollar amount of deficiency   $ (71,022 ) $ (91,857 )     $ (88,772 ) $ (66,633 ) $ (43,122 )

1




QuickLinks

RATIO OF EARNINGS TO FIXED CHARGES COGENT COMMUNICATIONS GROUP (000's)