The Calendar of the Vikings

As farmers, the Vikings divided the year into summer and winter halves. Each half was further divided into a number of weeks. Months were of less importance for farming.
For fishermen and navigators, though, the moon and the 'moons' (months) were important. Though the Viking calendar therefore might appear a little inconsistent, it perfectly served their needs.

The calendar which had developed from seasonal and climatic factors, divided the year simply into equal halves; winter and summer.
A man's age was counted not in years but in "winters", a custom which still applies to livestock. This would seem to indicate that the beginning of summer was regarded as a "new year", although there was no New year as such.
The year was also divided into lunar months. The counting of days was probably relatively inaccurate, especially in the summer months when the nights are bright in northern regions and it can be difficult to see the moon. Thus summer and winter were also divided into weeks, and periods of time were more likely to be counted in weeks than months.