When was 51 weeks ago from now?

There are 52 weeks and 1 day in a regular year and 52 weeks and 2 days in a leap year, so 51 weeks ago is 8 days less than a year ago if there is no leap year day during the past year. If there is a leap year day during the past year, 51 weeks ago is 9 days less than a year ago.

For example, if you are trying to calculate 51 weeks before October 1, 2014, you would subtract 1 year then add back 8 days (because 2014 is a regular year). So 51 weeks before October 1, 2014 is October 9, 2013.