feat: update amounts/percentages split logic to match OD (rework)

[ikevin127]

Explanation of Change

Note

Rework of PR #79273 which had 3 regressions listed below in tests.

In Classic, when a user splits an expense, we try to update the amounts for all splits to equal the amount of the original transaction automatically. We opted to go a simpler route with NewDot splits to start, avoiding any automatic updates, and punted adding this logic to a follow-up. This is that follow-up:

Problem: When users are editing the separate portions of a split they are typically trying to ensure all the portions add up to the original transaction amount.

Solution: Automatically change amounts and percentages when creating a split to add up to the original transaction amount to remove clicks/steps for the submitter. To do so, we'll implement our Classic logic:

Core logic:

• Default/unmodified values adjust automatically: Any split that hasn't been manually edited (i.e., still at its default value) will auto-adjust evenly so that all splits add up to 100% (for percentages) or the total amount (for amounts).
• Edited values are preserved: Once a user manually edits a percentage (or amount), that value is “locked in” and will never be auto-updated.
• Editing an initial split will preserve all Split values: We've added the ability to edit existing splits in NewDot and the individaul splits of an expense may be on different reports and in different states. To avoid complexity, when a user edits an amount or percentage on an existing split, we treat all splits as manually edited and stop auto-adjusting them.

Behavior for Adding Splits

• When a new split is added: Instead of defaulting to 0%, the system will redistribute all unedited splits automatically so they balance out to 100%.

Simple adding splits Example:

1. Submitter taps More Split on a $10 expense
2. Two initial splits exist at 50/50 = $5/$5
3. Submitter taps 'Add split'
4. A third split is added and the amounts are updated to 33%/33%/34% = $3.33/$3.33/$3.34

Further editing example:

1. Submitter taps More Split on a $10 expense
2. Two initial splits exist at 50/50 = $5/$5
3. Submitter edits Split A to $3.
4. Split B automatically updates to $7
5. Submitter taps 'Add split'
6. A third split is added. A remains $3, B updates to $3.50, the new split C is added as $3.50.

Error handling:

• Users can still manually override and push totals over/under 100%.
• In those cases, the same existing error message for invalid totals will be shown.

Fixed Issues

$ #70799
PROPOSAL:

Tests

Test 1: Adding Splits Auto-Redistributes

1. Create/find a $10 expense in a workspace.
2. Tap More > Split on the expense.
3. Verify initial splits show $5.00 / $5.00 (50/50).
4. Tap Add split.
5. Expected: Three splits show $3.33 / $3.33 / $3.34.
6. Edit Split A to $3.00.
7. Expected: Split B and C auto-update to $3.50 / $3.50.

Test 2: Edited Splits Stay Locked

1. Continue from Test 1 (A=$3, B=$3.50, C=$3.50).
2. Edit Split B to $4.00.
3. Expected: A stays $3, B stays $4, C redistributes to $3.00.
4. Add another split.
5. Expected: A=$3, B=$4 stay locked. C and D redistribute remaining $3.

Test 3: Editing Existing Saved Splits (All Locked)

1. Save a split expense with 2 splits.
2. Return to edit the splits.
3. Edit one split amount.
4. Expected: Only that split changes, no auto-redistribution.

🧪 (2) Regressions tests

1. Split - Split amounts do not auto redistribute after removing split #81251

• Go to workspace chat.
• Create an expense.
• Open the expense report.
• Click More > Split.
• Click Add split.
• Click Add split.
• Open any split.
• Click Remove split.
• Verify that split amounts will auto redistribute to match the total amount after removing split.

2. Split - Split amount field changes to NaN after clearing other split amount field #81241

• Go to workspace chat.
• Create an expense with negative amount.
• Open the expense report.
• Click More > Split.
• Click any split amount field.
• Clear the field but leave the negative sign.
• Verify that:
  • The other split amount field keeps its current value (no change)
  • No NaN is displayed anywhere
  • Additional verification:
    • After clearing to just -, type a complete number like -50 and verify the redistribution works correctly
    • Test with positive amounts as well to ensure normal functionality is not affected

• Verify that no errors appear in the JS console

Offline tests

Offline Test 1: Create Splits While Offline

1. Go offline.
2. Create a $20 expense split with 3 splits.
3. Edit one split while offline.
4. Go back online.
5. Expected: All changes sync correctly.

Offline Test 2: Add Split While Offline

1. Start with existing 2-split expense.
2. Go offline → Add a third split.
3. Expected: Auto-redistribution happens locally.
4. Go online → verify that changes sync correctly.

Offline Test 3: No Data Loss on Reconnect

1. Start split flow offline.
2. Make several edits.
3. Reconnect.
4. Expected: All local changes persist and sync.

QA Steps

Same as Tests.

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
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Screenshots/Videos

Android: HybridApp

android-hybrid.mp4

Android: mWeb Chrome

android-mweb.mp4

iOS: HybridApp

ios-hybrid.mov

iOS: mWeb Safari

ios-mweb.mov

MacOS: Chrome / Safari

web.mov

[melvin-bot]

@ShridharGoel Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

[ikevin127]

@ShridharGoel You can simply copy & paste the checklist from initial PR and only thing to do as reviewer is verify that the 3 regression tests listed in PR description are passing ✅

If it's a 🟢 pass you can approve and we can merge this again and hopefully no revert this time 🤞

[chatgpt-codex-connector]

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Codecov Report

❌ Looks like you've decreased code coverage for some files. Please write tests to increase, or at least maintain, the existing level of code coverage. See our documentation here for how to interpret this table.

Files with missing lines	Coverage Δ
...onList/ListItem/SplitListItem/SplitAmountInput.tsx	0.00% <ø> (ø)
src/components/MoneyRequestAmountInput.tsx	1.85% <0.00%> (-0.04%)	⬇️
...omponents/SelectionList/ListItem/SplitListItem.tsx	0.00% <0.00%> (ø)
src/components/NumberWithSymbolForm.tsx	2.76% <0.00%> (-0.05%)	⬇️
src/pages/iou/SplitExpensePage.tsx	0.00% <0.00%> (ø)
src/libs/actions/IOU/Split.ts	61.31% <68.96%> (+0.63%)	⬆️
... and 11 files with indirect coverage changes

[ShridharGoel]

Reviewer Checklist

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  • I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick).
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified any copy / text shown in the product is localized by adding it to src/languages/* files and using the translation method
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  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
  • I verified proper file naming conventions were followed for any new files or renamed files. All non-platform specific files are named after what they export and are not named "index.js". All platform-specific files are named for the platform the code supports as outlined in the README.
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Screenshots/Videos

Android: HybridApp

Screen.Recording.2026-01-24.at.12.30.24.PM.mov

Android: mWeb Chrome

Screen.Recording.2026-01-24.at.12.19.31.PM.mov

iOS: HybridApp

Screen.Recording.2026-01-24.at.12.33.53.PM.mov

iOS: mWeb Safari

Screen.Recording.2026-01-24.at.12.37.48.PM.mov

MacOS: Chrome / Safari

Screen.Recording.2026-01-22.at.1.25.02.AM.mov

[ShridharGoel]

It doesn't redistribute when editing splits, is that expected?

Screen.Recording.2026-02-06.at.4.36.52.PM.mov

[ShridharGoel]

Bug: Warning doesn't show when the total becomes greater than expected.

Screen.Recording.2026-02-06.at.4.40.14.PM.mov

[ShridharGoel]

It shows "Total amount is $21.00 less than the original expense." Shouldn't it be "Total amount is $21.00 greater than the original expense." ? Or are we comparing absolute values only?

[ikevin127]

It doesn't redistribute when editing splits, is that expected?

Yes, if the splits were manually edited by the user before, they won't be auto-redistributed whenever adding new ones / editing / removing - this is part of the original PRs tests where this is expected.

Bug: Warning doesn't show when the total becomes greater than expected.

✅ Addressed

It shows "Total amount is $21.00 less than the original expense." Shouldn't it be "Total amount is $21.00 greater than the original expense." ? Or are we comparing absolute values only?

I was comparing absolute values, but that deviated from staging behaviour so I reverted those specific changes to have preivous behaviour (staging) maintained ✅ (Total amount is $21.00 greater than the original expense.).

---

@ShridharGoel Please give it a final pass and let me know if everything works as expected 🙏

[ShridharGoel]

This still seems to have some issues.

-51+32 = -19 which is 3 greater than the expense. But the text says "lesser than".

[ikevin127]

@ShridharGoel Ok I think I got it (the AI not me), the greater than / less than issue should be resolved & properly aligned now - mind giving it another pass just to make sure ?

✅ I went back and made sure every previous case is corrected as well:

• feat: update amounts/percentages split logic to match OD (rework) #81626 (comment)
• feat: update amounts/percentages split logic to match OD (rework) #81626 (comment)
• feat: update amounts/percentages split logic to match OD (rework) #81626 (comment)
• feat: update amounts/percentages split logic to match OD (rework) #81626 (comment)

[ShridharGoel]

Bug: In edit mode, existing splits are now initialized with isManuallyEdited: true, which leads to an API call when saving without any changes in the split values. This does not lead to any API call on staging, so the behaviour has changed.

@blimpich Do you think this should be NAB (and handled in a follow-up if needed)?

Screen.Recording.2026-02-12.at.11.13.48.AM.mov

[ikevin127]

This was reported before by Codex, thought I fixed it already but there were conflicts due to refactoring and I probably reverted my changes without intention.

Hold on it, I'll check again!

[ikevin127]

@ShridharGoel I resolved this issue once again - mind taking a final pass at this ? 🙌

[ShridharGoel]

Seems to work well now

[github-actions]

🚧 @blimpich has triggered a test Expensify/App build. You can view the workflow run here.

[OSBotify]

✋ This PR was not deployed to staging yet because QA is ongoing. It will be automatically deployed to staging after the next production release.

[github-actions]

🧪🧪 Use the links below to test this adhoc build on Android, iOS, and Web. Happy testing! 🧪🧪
Built from App PR #81626.

Android 🤖	iOS 🍎
https://ad-hoc-expensify-cash.s3.us-east-1.amazonaws.com/rock-artifacts/ad-hoc/rock-android-Adhoc-a6eddbc160293664a88c8a1335a3ed2cb002ef6f/index.html	https://ad-hoc-expensify-cash.s3.us-east-1.amazonaws.com/rock-artifacts/ad-hoc/rock-ios-device-AdHoc-edaf6c7-cd605ac10e3975ad860bafa6593694216481276e/index.html

Web 🕸️
https://81626.pr-testing.expensify.com

---

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[OSBotify]

🚀 Deployed to staging by https://github.com/blimpich in version: 9.3.19-0 🚀

platform	result
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🤖 android 🤖	success ✅
🍎 iOS 🍎	success ✅

[nlemma]

@ikevin127 this PR is failing due to #82483

[OSBotify]

🚀 Deployed to production by https://github.com/mountiny in version: 9.3.19-5 🚀

platform	result
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🤖 android 🤖	success ✅
🍎 iOS 🍎	success ✅