fgo-docs

Buff actions values are calculated using the following formula:

num = buffAction.baseParam + (total plusTypes buffs values) - (total minusTypes buff values)

if buffAction.limit in (normal, lower):
    if num < 0:
        num = 0

num = num - buffAction.baseValue;

if buffAction.limit in (normal, upper):
    if maxRate < num:
        num = maxRate

return num

• Buff action variables can be found here:
• baseParam
• baseValue
• limit
• maxRate is a property of the buff item. This value can be found in the DB or API. If there are multiple buffs, the last maxRate is used. Different buffs of the same buff action usually have the same maxRate value.
• For example: we are trying to calculate cardMod with 10 level 10 Merlin's Hero Creation applied and no buster damage down:
• cardMod -> buff action commandAtk -> plusTypes buff type upCommandall
  • baseParam: 1000
  • baseValue: 0
  • limit: normal
  • maxRate: 5000
• num = 1000 + 500 * 10 = 6000 (baseParam = 1000 and there are 10 Hero Creation, each has Value of 500)
• limit is normal but num > 0 so lower bound is not applied
• num = num - baseValue = 6000 - 0 = 6000
• limit is normal and num > maxRate so upper bound is applied -> num = 5000
• The final cardMod value is 5000 or 500%.