Hey ​@Leyvis,

You might want to give the following formula a shot:
 

IF(
  {Start date},
  DATETIME_FORMAT(
    DATEADD(
      {Start date},
      IF(
        {Category} = "Playbooks",
        14,
        IF(
          {Category} = "How-to-Guides",
          3,
          0
        )
      ),
      'days'
    ),
    'MM/DD/YYYY'
  ),
  ""
)

 
Completely different matter, but would love to have you join our Airtable Hackathon! Make sure to sign up!!

Mike, Consultant @ Automatic Nation 
YouTube Channel 

I used SWITCH instead of nested IFs because it makes a bit more sense to me, but this should work…

IF({Start date}, 
  SWITCH(
    {Category}, 
    "Playbooks",DATETIME_FORMAT(DATEADD({Start date},14, 'days'),'MM/DD/YYYY'),
    "How-To-Guides", DATETIME_FORMAT(DATEADD({Start date},3, 'days'),'MM/DD/YYYY')), "") 

You can also add more categories pretty simply this way.

Yes, ​@DisraeliGears01 solution is way cleaner :D

Mike, Consultant @ Automatic Nation 
YouTube Channel

IF(
  {Start date},
  DATETIME_FORMAT(
    DATEADD(
      {Start date},
      IF(
        {Category} = "Playbooks",
        14,
        IF(
          {Category} = "How-to-Guides",
          3,
          0
        )
      ),
      'days'
    ),
    'MM/DD/YYYY'
  ),
  ""
)

Right on, it clarified how to include the additional If statements. Thank you. 

IF({Start date}, 
  SWITCH(
    {Category}, 
    "Playbooks",DATETIME_FORMAT(DATEADD({Start date},14, 'days'),'MM/DD/YYYY'),
    "How-To-Guides", DATETIME_FORMAT(DATEADD({Start date},3, 'days'),'MM/DD/YYYY')), "") 

So much cleaner approach and less thinking of all the parenthesis and commas. I will start playing with SWITCH.

A further addition!

IF(
  {Start Date}, 
  DATETIME_FORMAT(
    DATEADD(
      {Start Date},
      SWITCH(
        {Category}, 
        'Playbooks', 14,
        'How-To-Guides', 3
      ),
      'days'
    ),
    'MM/DD/YYYY'
  )
)