~$ vnstat -m

 eth0  /  monthly

       month        rx      |     tx      |    total    |   avg. rate
    ------------------------+-------------+-------------+---------------
      May '16      1.19 GiB |  724.19 MiB |    1.89 GiB |    5.93 kbit/s
      Jun '16      1.13 GiB |  362.17 MiB |    1.48 GiB |    4.80 kbit/s
      Jul '16    881.48 MiB |  332.49 MiB |    1.19 GiB |    3.71 kbit/s
      Aug '16      1.16 GiB |  605.96 MiB |    1.76 GiB |    5.50 kbit/s
      Sep '16      1.35 GiB |  759.63 MiB |    2.09 GiB |    6.77 kbit/s
      Oct '16      1.61 GiB |  986.44 MiB |    2.57 GiB |    8.05 kbit/s
      Nov '16      2.71 GiB |    3.19 GiB |    5.89 GiB |   19.07 kbit/s
      Dec '16      4.94 GiB |    4.80 GiB |    9.74 GiB |   30.52 kbit/s
      Jan '17      5.43 GiB |    4.99 GiB |   10.42 GiB |   32.63 kbit/s
      Feb '17      4.91 GiB |   11.52 GiB |   16.43 GiB |   56.99 kbit/s
      Mar '17      5.30 GiB |    4.85 GiB |   10.16 GiB |   31.81 kbit/s
      Apr '17      4.89 GiB |    6.36 GiB |   11.25 GiB |   39.82 kbit/s
    ------------------------+-------------+-------------+---------------
    estimated      5.34 GiB |    6.96 GiB |   12.30 GiB |