diff --git a/source/engine/treat.js b/source/engine/treat.js
index f47ff05ce..c575757bf 100644
--- a/source/engine/treat.js
+++ b/source/engine/treat.js
@@ -27,7 +27,8 @@ import { Node } from './mecanismViews/common'
 import {
 	treatVariable,
 	treatNegatedVariable,
-	treatFilteredVariable
+	treatFilteredVariable,
+	treatPeriodTransform
 } from './treatVariable'
 import { treat } from './traverse'
 import knownMecanisms from './known-mecanisms.yaml'
@@ -90,9 +91,13 @@ export let treatString = (rules, rule) => rawNode => {
 		)
 
 	if (parseResult.category == 'variable')
-		return treatVariable(rules, rule)(parseResult)
+		return treatPeriodTransform(rules, rule)(
+			treatVariable(rules, rule)(parseResult)
+		)
 	if (parseResult.category == 'filteredVariable')
-		return treatFilteredVariable(rules, rule)
+		return treatPeriodTransform(rules, rule)(
+			treatFilteredVariable(rules, rule)(parseResult)
+		)
 	if (parseResult.category == 'negatedVariable')
 		return treatNegatedVariable(
 			treatVariable(rules, rule)(parseResult.variable)
@@ -154,10 +159,19 @@ export let treatString = (rules, rule) => rawNode => {
 
 		let explanation = parseResult.explanation.map(
 				cond([
-					[propEq('category', 'variable'), treatVariable(rules, rule)],
+					[
+						propEq('category', 'variable'),
+						parseResult =>
+							treatPeriodTransform(rules, rule)(
+								treatVariable(rules, rule)(parseResult)
+							)
+					],
 					[
 						propEq('category', 'filteredVariable'),
-						treatFilteredVariable(rules, rule)
+						parseResult =>
+							treatPeriodTransform(rules, rule)(
+								treatFilteredVariable(rules, rule)(parseResult)
+							)
 					],
 					[
 						propEq('category', 'value'),
diff --git a/source/engine/treatVariable.js b/source/engine/treatVariable.js
index 5bb09ecb8..0022b8162 100644
--- a/source/engine/treatVariable.js
+++ b/source/engine/treatVariable.js
@@ -5,8 +5,9 @@ import { evaluateNode, rewriteNode, makeJsx } from './evaluation'
 import { getSituationValue } from './variables'
 import { Trans } from 'react-i18next'
 
-export let treatVariable = (rules, rule, filter) => parseResult => {
-	let variable = treatVariableTimeless(rules, rule, filter)(parseResult)
+// This function is a wrapper that can apply temporal transformations to the value of the variable.
+// See the période.yaml test suite for details
+export let treatPeriodTransform = (rules, rule) => variable => {
 	let evaluate = (cache, situation, parsedRules, node) => {
 		let explanation = evaluateNode(
 			cache,
@@ -55,7 +56,7 @@ export let treatVariable = (rules, rule, filter) => parseResult => {
 	}
 }
 
-export let treatVariableTimeless = (rules, rule, filter) => parseResult => {
+export let treatVariable = (rules, rule, filter) => parseResult => {
 	let evaluate = (cache, situation, parsedRules, node) => {
 		let dottedName = node.dottedName,
 			// On va vérifier dans le cache courant, dict, si la variable n'a pas été déjà évaluée
diff --git a/source/selectors/ficheDePaieSelectors.js b/source/selectors/ficheDePaieSelectors.js
index a50a44f75..452108fc6 100644
--- a/source/selectors/ficheDePaieSelectors.js
+++ b/source/selectors/ficheDePaieSelectors.js
@@ -123,8 +123,11 @@ const analysisToCotisations = (
 		'contrat salarié . cotisations patronales'
 	]
 		.map(name => analysis.cache[name])
+		// the last 'explanation' is because variables are wrapped in a period transform node
 		.map(pathOr([], ['explanation', 'formule', 'explanation', 'explanation']))
 		.reduce(concat, [])
+		.map(prop('explanation'))
+
 	const cotisations = pipe(
 		groupBy(prop('dottedName')),
 		values,