diff --git a/spec/System/TestSkills_spec.lua b/spec/System/TestSkills_spec.lua
index 66fe9623fd..d8fb3f90a2 100644
--- a/spec/System/TestSkills_spec.lua
+++ b/spec/System/TestSkills_spec.lua
@@ -490,6 +490,64 @@ describe("TestSkills", function()
 		assert.are.equals(9, finalCost) -- round(floor(9 * 1.5) / 1.5)
 	end)
 
+	it("converts positive flat Mana cost to partial Life cost", function()
+		build.skillsTab:PasteSocketGroup("Ball Lightning 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.are.equals(2, build.calcsTab.mainOutput.LifeCost)
+		assert.are.equals(11, build.calcsTab.mainOutput.ManaCost)
+	end)
+
+	it("converts positive flat Mana cost to full Life cost", function()
+		build.skillsTab:PasteSocketGroup("Ball Lightning 1/0  1\n")
+		build.configTab.input.customMods = "Skill Mana Costs Converted to Life Costs\n+4 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.are.equals(13, build.calcsTab.mainOutput.LifeCost)
+		assert.are.equals(0, build.calcsTab.mainOutput.ManaCost)
+	end)
+
+	it("does not convert negative flat Mana cost to partial Life cost", function()
+		build.skillsTab:PasteSocketGroup("Ball Lightning 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.are.equals(1, build.calcsTab.mainOutput.LifeCost)
+		assert.are.equals(1, build.calcsTab.mainOutput.ManaCost)
+	end)
+
+	it("does not convert negative flat Mana cost to full Life cost", function()
+		build.skillsTab:PasteSocketGroup("Ball Lightning 1/0  1\n")
+		build.configTab.input.customMods = "Skill Mana Costs Converted to Life Costs\nNon-Channelling Skills have -7 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+
+		assert.are.equals(9, build.calcsTab.mainOutput.LifeCost)
+		assert.are.equals(0, build.calcsTab.mainOutput.ManaCost)
+	end)
+
+	it("moves only positive flat Mana cost when skills cost Life instead", function()
+		build.skillsTab:PasteSocketGroup("Ball Lightning 1/0  1\n")
+		runCallback("OnFrame")
+		local baseManaCost = build.calcsTab.mainOutput.ManaCost
+
+		build.configTab.input.customMods = "Skills Cost Life instead of Mana\n+4 to Total Mana Cost"
+		build.configTab:BuildModList()
+		runCallback("OnFrame")
+		assert.are.equals(baseManaCost + 4, build.calcsTab.mainOutput.LifeCost)
+		assert.are.equals(0, build.calcsTab.mainOutput.ManaCost)
+
+		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.are.equals(baseManaCost, build.calcsTab.mainOutput.LifeCost)
+		assert.are.equals(0, build.calcsTab.mainOutput.ManaCost)
+	end)
+
 	it("Test socket group pasting with corruption levels and count", function()
 		build.skillsTab:PasteSocketGroup("Wave of Frost 20/0  3 C+1\n Culmination I 1/0  1")
 		assert.are.equals(3, build.skillsTab.socketGroupList[1].gemList[1].count)
diff --git a/src/Modules/CalcOffence.lua b/src/Modules/CalcOffence.lua
index 40425570cc..1c8ac6f040 100644
--- a/src/Modules/CalcOffence.lua
+++ b/src/Modules/CalcOffence.lua
@@ -2100,6 +2100,11 @@ function calcs.offence(env, actor, activeSkill)
 					val.baseCost = val.baseCost + costs[manaType].baseCost
 					val.baseCostNoMult = val.baseCostNoMult + costs[manaType].baseCostNoMult
 					val.finalBaseCost = val.finalBaseCost + costs[manaType].finalBaseCost
+					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
 					costs[manaType].baseCost = 0
 					costs[manaType].baseCostRaw = 0
 					costs[manaType].finalBaseCost = 0
@@ -2107,6 +2112,10 @@ function calcs.offence(env, actor, activeSkill)
 				elseif additionalLifeCost > 0 or hybridLifeCost > 0 then
 					val.baseCost = costs[manaType].baseCost
 					val.finalBaseCost = round(finalBaseCostRaw + round(costs[manaType].finalBaseCost * hybridLifeCost) + m_floor(val.baseCost * mult) * additionalLifeCost)
+					if val.upfront and hybridLifeCost > 0 then
+						-- Positive flat Mana cost is converted and rounded separately from the 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")