According to the law, military service begins at the beginning of the year in which a man turns 18 and continues until the end of the year in which he turns 60.

Women can participate in voluntary military service. The prerequisites are Finnish citizenship, 18–29 years of age and suitability for military training in terms of health and other personal characteristics. More than 12,000 Finnish women have completed voluntary military service. In 2024, more than 800 women were trained.

Military service is normally performed within the three years following the call-up between the ages of 19 to 21. A person liable for military service may apply for a transfer of the date and place of the start of the service for reasons of study, for example. However, the service must be completed by the time the person reaches the age of 30.

Conscripts enter military service in the Army, Navy and Air Force in two batches in January or July.

The military service lasts for 165, 255 or 347 days:

• The training period for those trained as officers, non-commissioned officers and for the most demanding special tasks is 347 days.
• The service time for people trained for tasks requiring special skills and professional competence is 255 days.
• The training for other tasks is 165 days.

During military service, conscripts are trained for national military defence tasks, thus creating the conditions for producing wartime troops. This requires general conscription and training of each conscript for wartime tasks that suit his or her abilities and inclinations.