New Feature: Add Make splits even functionality (rework - negative amount)

src/languages/de.ts

@@ -1131,6 +1131,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: 'Ausgabe aufteilen',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `${amount} von ${merchant}`,
         addSplit: 'Split hinzufügen',
+        makeSplitsEven: 'Aufteilungen angleichen',
         editSplits: 'Splits bearbeiten',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Der Gesamtbetrag ist ${amount} höher als die ursprüngliche Ausgabe.`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Der Gesamtbetrag ist ${amount} weniger als die ursprüngliche Ausgabe.`,

src/languages/en.ts

@@ -1117,6 +1117,7 @@ const translations = {
         splitExpense: 'Split expense',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `${amount} from ${merchant}`,
         addSplit: 'Add split',
+        makeSplitsEven: 'Make splits even',
         editSplits: 'Edit splits',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Total amount is ${amount} greater than the original expense.`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Total amount is ${amount} less than the original expense.`,

src/languages/es.ts

@@ -796,6 +796,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: 'Dividir gasto',
         splitExpenseSubtitle: ({amount, merchant}) => `${amount} de ${merchant}`,
         addSplit: 'Añadir división',
+        makeSplitsEven: 'Igualar divisiones',
         editSplits: 'Editar divisiones',
         totalAmountGreaterThanOriginal: ({amount}) => `El importe total es ${amount} mayor que el gasto original.`,
         totalAmountLessThanOriginal: ({amount}) => `El importe total es ${amount} menor que el gasto original.`,

src/languages/fr.ts

@@ -1133,6 +1133,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: 'Fractionner la dépense',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `${amount} de ${merchant}`,
         addSplit: 'Ajouter une répartition',
+        makeSplitsEven: 'Uniformiser les répartitions',
         editSplits: 'Modifier les répartitions',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Le montant total est de ${amount} supérieur à la dépense initiale.`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Le montant total est de ${amount} inférieur à la dépense originale.`,

src/languages/it.ts

@@ -1128,6 +1128,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: 'Dividi spesa',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `${amount} da ${merchant}`,
         addSplit: 'Aggiungi divisione',
+        makeSplitsEven: 'Uniformare le suddivisioni',
         editSplits: 'Modifica suddivisioni',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `L'importo totale è ${amount} maggiore della spesa originale.`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `L'importo totale è ${amount} inferiore alla spesa originale.`,

src/languages/ja.ts

@@ -1130,6 +1130,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: '経費を分割',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `${merchant}から${amount}`,
         addSplit: '分割を追加',
+        makeSplitsEven: '分割を均等にする',
         editSplits: '分割を編集',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `合計金額は元の経費よりも${amount}多いです。`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `合計金額は元の経費よりも${amount}少なくなっています。`,

src/languages/nl.ts

@@ -1128,6 +1128,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: 'Uitgave splitsen',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `${amount} van ${merchant}`,
         addSplit: 'Splits toevoegen',
+        makeSplitsEven: 'Verdelingen gelijk maken',
         editSplits: 'Splits bewerken',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Het totale bedrag is ${amount} meer dan de oorspronkelijke uitgave.`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Het totale bedrag is ${amount} minder dan de oorspronkelijke uitgave.`,

src/languages/pl.ts

@@ -1127,6 +1127,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: 'Podziel wydatek',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `${amount} od ${merchant}`,
         addSplit: 'Dodaj podział',
+        makeSplitsEven: 'Wyrównaj podziały',
         editSplits: 'Edytuj podziały',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Całkowita kwota jest o ${amount} większa niż pierwotny wydatek.`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `Całkowita kwota jest o ${amount} mniejsza niż pierwotny wydatek.`,

src/languages/pt-BR.ts

@@ -1128,6 +1128,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: 'Dividir despesa',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `${amount} de ${merchant}`,
         addSplit: 'Adicionar divisão',
+        makeSplitsEven: 'Tornar as divisões iguais',
         editSplits: 'Editar divisões',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `O valor total é ${amount} maior que a despesa original.`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `O valor total é ${amount} a menos que a despesa original.`,

src/languages/zh-hans.ts

@@ -1116,6 +1116,7 @@ const translations: TranslationDeepObject<typeof en> = {
         splitExpense: '拆分费用',
         splitExpenseSubtitle: ({amount, merchant}: SplitExpenseSubtitleParams) => `来自${merchant}的${amount}`,
         addSplit: '添加分账',
+        makeSplitsEven: '使拆分均等',
         editSplits: '编辑拆分',
         totalAmountGreaterThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `总金额比原始费用多${amount}。`,
         totalAmountLessThanOriginal: ({amount}: TotalAmountGreaterOrLessThanOriginalParams) => `总金额比原始费用少 ${amount}。`,

src/libs/IOUUtils.ts

@@ -53,19 +53,33 @@ function navigateToParticipantPage(iouType: ValueOf<typeof CONST.IOU.TYPE>, tran
 }
 
 /**
- * Calculates the amount per user given a list of participants
+ * Calculates the amount per split.
  *
- * @param numberOfParticipants - Number of participants in the chat. It should not include the current user.
+ * @param numberOfSplits - Number of splits EXCLUDING the remainder holder ("default user").
  * @param total - IOU total amount in backend format (cents, no matter the currency)
- * @param currency - This is used to know how many decimal places are valid to use when splitting the total
- * @param isDefaultUser - Whether we are calculating the amount for the current user
+ * @param currency - Used to know how many decimal places are valid when splitting the total
+ * @param isDefaultUser - Whether we are calculating the amount for the remainder holder
+ * @param useFloorToLastRounding - `false` (default, legacy behavior) or `true` to floor all and put full remainder on the default user
  */
-function calculateAmount(numberOfParticipants: number, total: number, currency: string, isDefaultUser = false): number {
+function calculateAmount(numberOfSplits: number, total: number, currency: string, isDefaultUser = false, useFloorToLastRounding = false): number {
     // Since the backend can maximum store 2 decimal places, any currency with more than 2 decimals
     // has to be capped to 2 decimal places
     const currencyUnit = Math.min(100, getCurrencyUnit(currency));
     const totalInCurrencySubunit = (total / 100) * currencyUnit;
-    const totalParticipants = numberOfParticipants + 1;
+    const totalParticipants = numberOfSplits + 1;
+
+    // New optional mode
+    if (useFloorToLastRounding) {
+        // For positive totals, floor for everyone and add the full remainder to the default user
+        // For negative totals, do the inverse of above and round up using Math.ceil to calculate the base share
+        const baseShareSubunit = totalInCurrencySubunit >= 0 ? Math.floor(totalInCurrencySubunit / totalParticipants) : Math.ceil(totalInCurrencySubunit / totalParticipants);
+        const remainderSubunit = totalInCurrencySubunit - baseShareSubunit * totalParticipants;
+
+        const subunitAmount = baseShareSubunit + (isDefaultUser ? remainderSubunit : 0);
+        return Math.round((subunitAmount * 100) / currencyUnit);
+    }
+
+    // Legacy behavior (backwards compatible): round equally and adjust default user by +/- difference
     const amountPerPerson = Math.round(totalInCurrencySubunit / totalParticipants);
     let finalAmount = amountPerPerson;
     if (isDefaultUser) {

src/libs/actions/IOU.ts

@@ -694,7 +694,7 @@
 };
 
 let allPersonalDetails: OnyxTypes.PersonalDetailsList = {};
 Onyx.connect({
     key: ONYXKEYS.PERSONAL_DETAILS_LIST,
     callback: (value) => {
         allPersonalDetails = value ?? {};
@@ -771,13 +771,13 @@
 };
 
 let allBetas: OnyxEntry<OnyxTypes.Beta[]>;
 Onyx.connect({
     key: ONYXKEYS.BETAS,
     callback: (value) => (allBetas = value),
 });
 
 let allTransactions: NonNullable<OnyxCollection<OnyxTypes.Transaction>> = {};
 Onyx.connect({
     key: ONYXKEYS.COLLECTION.TRANSACTION,
     waitForCollectionCallback: true,
     callback: (value) => {
@@ -791,7 +791,7 @@
 });
 
 let allTransactionDrafts: NonNullable<OnyxCollection<OnyxTypes.Transaction>> = {};
 Onyx.connect({
     key: ONYXKEYS.COLLECTION.TRANSACTION_DRAFT,
     waitForCollectionCallback: true,
     callback: (value) => {
@@ -800,7 +800,7 @@
 });
 
 let allTransactionViolations: NonNullable<OnyxCollection<OnyxTypes.TransactionViolations>> = {};
 Onyx.connect({
     key: ONYXKEYS.COLLECTION.TRANSACTION_VIOLATIONS,
     waitForCollectionCallback: true,
     callback: (value) => {
@@ -814,7 +814,7 @@
 });
 
 let allNextSteps: NonNullable<OnyxCollection<OnyxTypes.ReportNextStep>> = {};
 Onyx.connect({
     key: ONYXKEYS.COLLECTION.NEXT_STEP,
     waitForCollectionCallback: true,
     callback: (value) => {
@@ -823,7 +823,7 @@
 });
 
 const allPolicies: OnyxCollection<OnyxTypes.Policy> = {};
 Onyx.connect({
     key: ONYXKEYS.COLLECTION.POLICY,
     callback: (val, key) => {
         if (!key) {
@@ -842,14 +842,14 @@
 // `allRecentlyUsedTags` was moved here temporarily from `src/libs/actions/Policy/Tag.ts` during the `Deprecate Onyx.connect` refactor.
 // All uses of this variable should be replaced with `useOnyx`.
 let allRecentlyUsedTags: OnyxCollection<RecentlyUsedTags> = {};
 Onyx.connect({
     key: ONYXKEYS.COLLECTION.POLICY_RECENTLY_USED_TAGS,
     waitForCollectionCallback: true,
     callback: (val) => (allRecentlyUsedTags = val),
 });
 
 let allReports: OnyxCollection<OnyxTypes.Report>;
 Onyx.connect({
     key: ONYXKEYS.COLLECTION.REPORT,
     waitForCollectionCallback: true,
     callback: (value) => {
@@ -858,7 +858,7 @@
 });
 
 let allReportNameValuePairs: OnyxCollection<OnyxTypes.ReportNameValuePairs>;
 Onyx.connect({
     key: ONYXKEYS.COLLECTION.REPORT_NAME_VALUE_PAIRS,
     waitForCollectionCallback: true,
     callback: (value) => {
@@ -13612,6 +13612,47 @@
     });
 }
 
+/**
+ * Evenly distribute the draft split expense amounts across all split items.
+ * Remainders are added to the first or last item to ensure the total matches the original amount.
+ *
+ * Notes:
+ * - Works entirely on the provided `draftTransaction` to avoid direct Onyx reads.
+ * - Uses `calculateAmount` utility to handle currency subunits and rounding consistently with existing logic.
+ */
+function evenlyDistributeSplitExpenseAmounts(draftTransaction: OnyxEntry<OnyxTypes.Transaction>) {
+    if (!draftTransaction) {
+        return;
+    }
+
+    const originalTransactionID = draftTransaction?.comment?.originalTransactionID;
+    const splitExpenses = draftTransaction?.comment?.splitExpenses ?? [];
+    const currency = getCurrency(draftTransaction);
+
+    // Use allowNegative=true and disableOppositeConversion=true to preserve original amount sign
+    const total = getAmount(draftTransaction, undefined, undefined, true, true);
+
+    // Guard clause for missing data
+    if (!originalTransactionID || splitExpenses.length === 0) {
+        return;
+    }
+
+    // Floor-allocation with full remainder added to the last split so the last is always the largest
+    const splitCount = splitExpenses.length;
+    const lastIndex = splitCount - 1;
+
+    const updatedSplitExpenses = splitExpenses.map((splitExpense, index) => ({
+        ...splitExpense,
+        amount: calculateIOUAmount(splitCount - 1, total, currency, index === lastIndex, true),
+    }));
+
+    Onyx.merge(`${ONYXKEYS.COLLECTION.SPLIT_TRANSACTION_DRAFT}${originalTransactionID}`, {
+        comment: {
+            splitExpenses: updatedSplitExpenses,
+        },
+    });
+}
+
 function removeSplitExpenseField(draftTransaction: OnyxEntry<OnyxTypes.Transaction>, splitExpenseTransactionID: string) {
     if (!draftTransaction || !splitExpenseTransactionID) {
         return;
@@ -14360,6 +14401,7 @@
     initSplitExpense,
     initSplitExpenseItemData,
     addSplitExpenseField,
+    evenlyDistributeSplitExpenseAmounts,
     updateSplitExpenseAmountField,
     updateSplitTransactions,
     updateSplitTransactionsFromSplitExpensesFlow,

src/pages/iou/SplitExpensePage.tsx

@@ -8,6 +8,7 @@ import ConfirmModal from '@components/ConfirmModal';
 import FormHelpMessage from '@components/FormHelpMessage';
 import HeaderWithBackButton from '@components/HeaderWithBackButton';
 import * as Expensicons from '@components/Icon/Expensicons';
+import MenuItem from '@components/MenuItem';
 import ScreenWrapper from '@components/ScreenWrapper';
 import {useSearchContext} from '@components/Search/SearchContext';
 import SelectionList from '@components/SelectionListWithSections';
@@ -22,6 +23,7 @@ import useThemeStyles from '@hooks/useThemeStyles';
 import {
     addSplitExpenseField,
     clearSplitTransactionDraftErrors,
+    evenlyDistributeSplitExpenseAmounts,
     getIOUActionForTransactions,
     getIOURequestPolicyID,
     initDraftSplitExpenseDataForEdit,
@@ -115,6 +117,13 @@ function SplitExpensePage({route}: SplitExpensePageProps) {
         addSplitExpenseField(transaction, draftTransaction);
     }, [draftTransaction, transaction, transactionID]);
 
+    const onMakeSplitsEven = useCallback(() => {
+        if (!draftTransaction) {
+            return;
+        }
+        evenlyDistributeSplitExpenseAmounts(draftTransaction);
+    }, [draftTransaction]);
+
     const onSaveSplitExpense = useCallback(() => {
         if (splitExpenses.length <= 1 && !childTransactions.length) {
             const splitFieldDataFromOriginalTransactionWithoutID = {...splitFieldDataFromOriginalTransaction, transactionID: ''};
@@ -279,31 +288,35 @@ function SplitExpensePage({route}: SplitExpensePageProps) {
         getTranslatedText,
     ]);
 
-    const headerContent = useMemo(
-        () => (
-            <View style={[styles.w100, styles.ph5, styles.flexRow, styles.gap2, shouldUseNarrowLayout && styles.mb3]}>
-                <Button
-                    success
+    const listFooterContent = useMemo(() => {
+        const shouldShowMakeSplitsEven = childTransactions.length === 0;
+        return (
+            <View style={[styles.w100, styles.flexColumn, styles.mt1, shouldUseNarrowLayout && styles.mb3]}>
+                <MenuItem
                     onPress={onAddSplitExpense}
+                    title={translate('iou.addSplit')}
                     icon={Expensicons.Plus}
-                    text={translate('iou.addSplit')}
-                    style={[shouldUseNarrowLayout && styles.flex1]}
+                    style={[styles.ph4]}
                 />
+                {shouldShowMakeSplitsEven && (
+                    <MenuItem
+                        onPress={onMakeSplitsEven}
+                        title={translate('iou.makeSplitsEven')}
+                        icon={Expensicons.ArrowsLeftRight}
+                        style={[styles.ph4]}
+                    />
+                )}
             </View>
-        ),
-        [onAddSplitExpense, shouldUseNarrowLayout, styles.flex1, styles.flexRow, styles.gap2, styles.mb3, styles.ph5, styles.w100, translate],
-    );
+        );
+    }, [onAddSplitExpense, onMakeSplitsEven, translate, childTransactions, shouldUseNarrowLayout, styles.w100, styles.ph4, styles.flexColumn, styles.mt1, styles.mb3]);
 
     const footerContent = useMemo(() => {
         const shouldShowWarningMessage = sumOfSplitExpenses < transactionDetailsAmount;
         const warningMessage = shouldShowWarningMessage
             ? translate('iou.totalAmountLessThanOriginal', {amount: convertToDisplayString(transactionDetailsAmount - sumOfSplitExpenses, transactionDetails.currency)})
             : '';
         return (
-            <View
-                ref={footerRef}
-                style={styles.pt3}
-            >
+            <View ref={footerRef}>
                 {(!!errorMessage || !!warningMessage) && (
                     <FormHelpMessage
                         style={[styles.ph1, styles.mb2]}
@@ -323,7 +336,7 @@ function SplitExpensePage({route}: SplitExpensePageProps) {
                 />
             </View>
         );
-    }, [sumOfSplitExpenses, transactionDetailsAmount, translate, transactionDetails.currency, errorMessage, styles.ph1, styles.mb2, styles.w100, onSaveSplitExpense, styles.pt3, footerRef]);
+    }, [sumOfSplitExpenses, transactionDetailsAmount, translate, transactionDetails.currency, errorMessage, styles.ph1, styles.mb2, styles.w100, onSaveSplitExpense, footerRef]);
 
     const initiallyFocusedOptionKey = useMemo(
         () => sections.at(0)?.data.find((option) => option.transactionID === splitExpenseTransactionID)?.keyForList,
@@ -375,12 +388,12 @@ function SplitExpensePage({route}: SplitExpensePageProps) {
                             });
                         }}
                         ref={listRef}
-                        headerContent={headerContent}
                         sections={sections}
                         initiallyFocusedOptionKey={initiallyFocusedOptionKey}
                         ListItem={SplitListItem}
-                        containerStyle={[styles.flexBasisAuto, styles.pt1]}
+                        containerStyle={[styles.flexBasisAuto]}
                         footerContent={footerContent}
+                        listFooterContent={listFooterContent}
                         disableKeyboardShortcuts
                         shouldSingleExecuteRowSelect
                         canSelectMultiple={false}