On average, one bottle of face oil lasts around 2-6 months, depending on your usage.
If you have very dry skin, you might use more oil per application.
If you use one bottle for both morning and night-time use every day, your bottle will likely last 2-4 months.
If you're purchasing the Day & Night Duo which has 2 different bottles for morning and night-time use, it will likely last you between 3-6 months.