diff --git a/spec/System/TestSkills_spec.lua b/spec/System/TestSkills_spec.lua
index af8896f64c..db61b6ffa4 100644
--- a/spec/System/TestSkills_spec.lua
+++ b/spec/System/TestSkills_spec.lua
@@ -381,6 +381,46 @@ describe("TestSkills", function()
 		assert.equals(18, build.calcsTab.mainOutput.LifeCost)
 	end)
 
+	it("converts and rounds flat mana cost separately from base cost", function()
+		build.skillsTab:PasteSocketGroup("Hydrosphere 1/0  1\n")
+		build.configTab.input.customMods = "Skills Cost Life instead of 15% of Mana Cost\n+4 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.equals(3, build.calcsTab.mainOutput.LifeCost)
+		assert.equals(13, build.calcsTab.mainOutput.ManaCost)
+	end)
+
+	it("moves flat mana cost when all costs are converted", function()
+		build.skillsTab:PasteSocketGroup("Hydrosphere 1/0  1\n")
+		build.configTab.input.customMods = "Skills Cost Life instead of Mana\n+4 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.equals(16, build.calcsTab.mainOutput.LifeCost)
+		assert.equals(0, build.calcsTab.mainOutput.ManaCost)
+	end)
+
+	it("does not move reduced flat mana cost to life", function()
+		build.skillsTab:PasteSocketGroup("Hydrosphere 1/0  1\n")
+		build.configTab.input.customMods = "Skills Cost Life instead of Mana\nNon-Channelling Skills have -7 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.equals(12, build.calcsTab.mainOutput.LifeCost)
+		assert.equals(0, build.calcsTab.mainOutput.ManaCost)
+	end)
+
+	it("does not partially convert reduced flat mana cost to life", function()
+		build.skillsTab:PasteSocketGroup("Hydrosphere 1/0  1\n")
+		build.configTab.input.customMods = "Skills Cost Life instead of 15% of Mana Cost\nNon-Channelling Skills have -7 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.equals(2, build.calcsTab.mainOutput.LifeCost)
+		assert.equals(4, build.calcsTab.mainOutput.ManaCost)
+	end)
+
 	it("Test flat cost is added after cost efficiency for energy shield costs", function()
 		build.skillsTab:PasteSocketGroup("Hydrosphere 1/0  1\n")
 
@@ -392,6 +432,26 @@ describe("TestSkills", function()
 		-- 12 / 1.5 + 10 = 18
 		assert.equals(18, build.calcsTab.mainOutput.ESCost)
 	end)
+
+	it("moves flat mana cost to energy shield with the base cost", function()
+		build.skillsTab:PasteSocketGroup("Hydrosphere 1/0  1\n")
+		build.configTab.input.customMods = "Skills Cost Energy Shield instead of Mana or Life\n+4 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.equals(16, build.calcsTab.mainOutput.ESCost)
+		assert.equals(0, build.calcsTab.mainOutput.ManaCost)
+	end)
+
+	it("does not move reduced flat mana cost to energy shield", function()
+		build.skillsTab:PasteSocketGroup("Hydrosphere 1/0  1\n")
+		build.configTab.input.customMods = "Skills Cost Energy Shield instead of Mana or Life\nNon-Channelling Skills have -7 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.equals(12, build.calcsTab.mainOutput.ESCost)
+		assert.equals(0, build.calcsTab.mainOutput.ManaCost)
+	end)
 	it("Test mana cost efficiency with support gems", function()
 		-- Test interaction between cost efficiency and cost multipliers
 		build.skillsTab:PasteSocketGroup("Contagion 6/0  1\nMagnified Area I 1/0  1")
diff --git a/src/Modules/CalcOffence.lua b/src/Modules/CalcOffence.lua
index 3fd3f028e3..68d6d21735 100644
--- a/src/Modules/CalcOffence.lua
+++ b/src/Modules/CalcOffence.lua
@@ -1707,6 +1707,11 @@ function calcs.offence(env, actor, activeSkill)
 			if val.type == "Life" then
 				local manaType = resource:gsub("Life", "Mana")
 				if skillModList:Flag(skillCfg, "CostLifeInsteadOfMana") then -- Blood Magic / Lifetap
+					if val.upfront then
+						local manaTotalCost = skillModList:Sum("BASE", skillCfg, manaType.."Cost")
+						val.totalCost = val.totalCost + m_max(0, manaTotalCost)
+						costs[manaType].totalCost = costs[manaType].totalCost - manaTotalCost
+					end
 					val.baseCost = val.baseCost + costs[manaType].baseCost
 					val.baseCostNoMult = val.baseCostNoMult + costs[manaType].baseCostNoMult
 					val.finalBaseCost = val.finalBaseCost + costs[manaType].finalBaseCost
@@ -1717,11 +1722,22 @@ function calcs.offence(env, actor, activeSkill)
 				elseif (additionalLifeCost > 0 or hybridLifeCost > 0) and not skillModList:Flag(skillCfg, "CostESInsteadOfManaOrLife") then
 					val.baseCost = costs[manaType].baseCost
 					val.finalBaseCost = val.finalBaseCost + round(costs[manaType].finalBaseCost * (hybridLifeCost + additionalLifeCost))
+					if val.upfront and hybridLifeCost > 0 then
+						-- Only positive flat mana cost is converted, and it is rounded separately from base cost.
+						val.totalCost = val.totalCost + round(m_max(0, skillModList:Sum("BASE", skillCfg, manaType.."Cost")) * hybridLifeCost)
+					end
 				end
 			elseif val.type == "ES" then
 				local manaType = resource:gsub("ES", "Mana")
 				local lifeType = resource:gsub("ES", "Life")
 			  	if skillModList:Flag(skillCfg, "CostESInsteadOfManaOrLife") then -- Whispers of Infinity
+					if val.upfront then
+						local manaTotalCost = skillModList:Sum("BASE", skillCfg, manaType.."Cost")
+						local lifeTotalCost = skillModList:Sum("BASE", skillCfg, lifeType.."Cost")
+						val.totalCost = val.totalCost + m_max(0, manaTotalCost) + m_max(0, lifeTotalCost)
+						costs[manaType].totalCost = costs[manaType].totalCost - manaTotalCost
+						costs[lifeType].totalCost = costs[lifeType].totalCost - lifeTotalCost
+					end
 					val.baseCost = val.baseCost + costs[manaType].baseCost+ costs[lifeType].baseCost
 					val.baseCostNoMult = val.baseCostNoMult + costs[manaType].baseCostNoMult + costs[lifeType].baseCostNoMult
 					val.finalBaseCost = val.finalBaseCost + costs[manaType].finalBaseCost + costs[lifeType].finalBaseCost