To find a relative date 8 weeks in the future from 13th January, you need to add 8 weeks to the given date. First, convert 8 weeks to days (1 week = 7 days), which is 56 days. Then, add 56 days to 13th January.

To calculate manually:

1. Start with 13th January.
2. Add 56 days, which brings you to 8th March.
Therefore, 8 weeks in the future from the 13th of January is the 8th of March.