give_piety_reward_effect

give_piety_reward_effect = {
	add_piety = {
		value = $LENGTH$_pilgrimage_piety_gain
		# Multipliers
		## How seriously are you taking this pilgrimage?
		### Not very.
		if = {
			limit = {
				root.involved_activity = {
					has_activity_option = {
						category = pilgrimage_option_fidelity
						option = pilgrimage_fidelity_obligatory
					}
				}
			}
			multiply = 0.5
		}
		### Thuper theriouthe.
		else_if = {
			limit = {
				root.involved_activity = {
					has_activity_option = {
						category = pilgrimage_option_fidelity
						option = pilgrimage_fidelity_contemplative
					}
				}
			}
			multiply = 1.25
		}
		## Depending on how well you clung to your intent, you may get a higher reward.
		if = {
			limit = { has_character_flag = perfect_pious_reward }
			multiply = pilgrimage_perfect_pious_multiplier
		}
		else_if = {
			limit = { has_character_flag = high_pious_reward }
			multiply = pilgrimage_high_pious_multiplier
		}
		else_if = {
			limit = { has_character_flag = mid_pious_reward }
			multiply = pilgrimage_mid_pious_multiplier
		}
		else_if = {
			limit = { has_character_flag = low_pious_reward }
			multiply = pilgrimage_low_pious_multiplier
		}
		# Additives
		## Experienced pilgrims may get more piety overall.
		if = {
			limit = { has_character_flag = should_get_trait_piety }
			add = minor_piety_gain
		}
		## Certain activity options may give you more piety also.
		if = {
			limit = {
				root.involved_activity = {
					OR = {
						has_activity_option = {
							category = pilgrimage_option_pomp
							option = pilgrimage_pomp_humble
						}
						has_activity_option = {
							category = pilgrimage_option_pomp
							option = pilgrimage_pomp_ceremonial
						}
					}
				}
			}
			add = minor_piety_gain
		}
		else_if = {
			limit = {
				root.involved_activity = {
					has_activity_option = {
						category = pilgrimage_option_pomp
						option = pilgrimage_pomp_throng
					}
				}
			}
			add = medium_piety_gain
		}
		if = {
			limit = {
				root.rite = { rite_has_parameter = tenet_inner_journey_humble_pilgrimage_bonus }
				root.involved_activity = {
					has_activity_option = {
						category = pilgrimage_option_pomp
						option = pilgrimage_pomp_humble
					}
				}
			}
			multiply = 1.5
		}
		# Regular Holy Sites give less 50% less
		if = {
			limit = {
				root.faith = {
					any_holy_site = {
						is_eminent = no
						holy_site_county = root.involved_activity.activity_location.county
					}
				}
			}
			multiply = 0.5
		}
		# Final multipliers
		if = {
			limit = {
				root.confederation ?= { has_cohesion_level_parameter = any_member_increased_pilgrimage_rewards }
			}
			multiply = 1.1
		}
	}
}

As written in game/common/scripted_effects/00_pilgrimage_effects.txt.