I see that you say these last 3-4 months. Is that assuming they are worn once a week, or does the frequency that they are worn even factor in to this?

The frequency with which the socks are worn is not a factor. Although it is recommendable to buy two socks, that way you can alternate them between days. The reason we ask you to change them every 3–4 months is because the life span of the compression in the socks wears out over time.