From 96d9559ebe4d837c027dbca4a39899db08ea746c Mon Sep 17 00:00:00 2001
From: Chris Fiel <ccfiel@gmail.com>
Date: Fri, 15 May 2026 15:37:31 +0800
Subject: [PATCH] Fix/SELL fee added to cash balance instead of subtracted
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When creating a SELL activity with a non-zero fee, the cash balance on
the account was credited by (quantity * unitPrice) + fee instead of
(quantity * unitPrice) - fee, inflating the cash balance by 2x the fee.

The previous logic added the fee to the gross magnitude before negating
the entire amount for BUY/FEE. SELL (and DIVIDEND/INTEREST/LIABILITY
when carrying a fee) therefore received +gross + fee.

Compute the signed gross amount first, then subtract the fee
unconditionally — fees always reduce cash regardless of activity
direction.
---
 CHANGELOG.md                                      | 6 ++++++
 apps/api/src/app/activities/activities.service.ts | 8 ++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f23e1af95..363c224c6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+
+- Fixed the cash balance computation for `SELL` activities to subtract the fee instead of adding it (the previous logic inflated the account's cash balance by twice the fee)
+
 ## 3.3.0 - 2026-05-14
 
 ### Added
diff --git a/apps/api/src/app/activities/activities.service.ts b/apps/api/src/app/activities/activities.service.ts
index 58b9c11a4..95e5aa05b 100644
--- a/apps/api/src/app/activities/activities.service.ts
+++ b/apps/api/src/app/activities/activities.service.ts
@@ -214,15 +214,15 @@ export class ActivitiesService {
     });
 
     if (updateAccountBalance === true) {
-      let amount = new Big(data.unitPrice)
-        .mul(data.quantity)
-        .plus(data.fee)
-        .toNumber();
+      let amount = new Big(data.unitPrice).mul(data.quantity).toNumber();
 
       if (['BUY', 'FEE'].includes(data.type)) {
         amount = new Big(amount).mul(-1).toNumber();
       }
 
+      // Fees always reduce cash regardless of the activity direction
+      amount = new Big(amount).minus(data.fee).toNumber();
+
       await this.accountService.updateAccountBalance({
         accountId,
         amount,