fix: correct tax slabs to match NBR official documentation

Issues fixed:
- Remove incorrect 30% tax rate for FY 2024-2025 (should end at 25%)
- Correct FY 2025-2026 tax structure to match NBR official:
  - First slab corrected from 3.75 lakh to 3.5 lakh
  - Added missing 5% tax bracket [3.5-4.5 lakh]
  - Updated all thresholds to match 2024-2025 structure
- Update all unit tests to reflect correct tax structure

Fixes #44

Co-authored-by: Nadim Tuhin <nadimtuhin@users.noreply.github.com>

Author: github-actions[bot]

src/utils/taxSlabs.js

@@ -1,8 +1,8 @@
 const LAKH = 100000;
 
 // Bangladesh Tax Slab Structure (amounts in lakh)
-const TAX_SLAB_AMOUNTS = [1, 4, 5, 5, 20]; // After threshold: 1L, 4L, 5L, 5L, 20L
-const TAX_RATES = [0, 5, 10, 15, 20, 25, 30]; // 0% for threshold, then 5%, 10%, etc.
+const TAX_SLAB_AMOUNTS = [1, 4, 5, 5]; // After threshold: 1L, 4L, 5L, 5L
+const TAX_RATES = [0, 5, 10, 15, 20, 25]; // 0% for threshold, then 5%, 10%, 15%, 20%, 25%
 
 const formatLakh = (lakhs) => {
   return lakhs === Math.floor(lakhs) ? `${lakhs}` : `${lakhs.toFixed(1)}`;

src/utils/taxSlabs2025.js

@@ -1,9 +1,9 @@
 const LAKH = 100000;
 
 // Bangladesh Tax Slab Structure FY 2025-2026 (amounts in lakh)
-// Note: 5% bracket has been removed, structure simplified to 6 slabs
-const TAX_SLAB_AMOUNTS_2025 = [3, 4, 5, 20]; // After threshold: 3L, 4L, 5L, 20L
-const TAX_RATES_2025 = [0, 10, 15, 20, 25, 30]; // 0% for threshold, then 10%, 15%, etc. (no 5%)
+// Based on NBR official documentation - same structure as FY 2024-2025
+const TAX_SLAB_AMOUNTS_2025 = [1, 4, 5, 5]; // After threshold: 1L, 4L, 5L, 5L
+const TAX_RATES_2025 = [0, 5, 10, 15, 20, 25]; // 0% for threshold, then 5%, 10%, 15%, 20%, 25%
 
 const formatLakh = (lakhs) => {
   return lakhs === Math.floor(lakhs) ? `${lakhs}` : `${lakhs.toFixed(1)}`;
@@ -54,16 +54,16 @@ export function calculateTaxSlabs2025(taxFreeThreshold) {
 
 /**
  * Get tax-free thresholds for FY 2025-2026
- * Updated thresholds: +25,000 BDT across all categories
+ * Based on NBR official documentation
  */
 export const TAX_FREE_THRESHOLDS_2025 = {
-  general: 375000,        // +25K from 350K
-  female: 425000,         // +25K from 400K
-  senior: 425000,         // +25K from 400K (65+ years)
-  disabled: 500000,       // +25K from 475K
-  third_gender: 500000,   // +25K from 475K
-  freedom_fighter: 525000, // +25K from 500K
-  parent_disabled: 425000  // 375K + 50K exemption
+  general: 350000,        // 3.5 lakh
+  female: 400000,         // 4.0 lakh
+  senior: 400000,         // 4.0 lakh (65+ years)
+  disabled: 475000,       // 4.75 lakh
+  third_gender: 475000,   // 4.75 lakh
+  freedom_fighter: 500000, // 5.0 lakh
+  parent_disabled: 400000  // 4.0 lakh
 };
 
 /**

tests/unit/calculation2025.test.js

@@ -80,13 +80,13 @@ describe('Calculation-2025 Component', () => {
       expect(totalTaxDisplay.text()).toContain(wrapper.vm.totalTax.toString());
     });
 
-    test('should use FY 2025-26 tax slabs (6 slabs, no 5% bracket)', () => {
+    test('should use FY 2025-26 tax slabs (7 slabs, includes 5% bracket)', () => {
       store.commit('updateTaxpayerProfile', {
         category: 'general',
         age: 30,
         location: 'dhaka'
       });
-      
+
       store.commit('changeSubsequentSalaries', { index: 0, value: 50000 }); // 600K annually
 
       wrapper = mount(Calculation2025, {
@@ -96,16 +96,16 @@ describe('Calculation-2025 Component', () => {
       });
 
       const taxBreakdown = wrapper.vm.taxBreakdown;
-      
-      expect(taxBreakdown).toHaveLength(6); // 6 slabs for 2025-26
-      
-      // Check that tax rates don't include 5%
+
+      expect(taxBreakdown).toHaveLength(7); // 7 slabs for 2025-26
+
+      // Check that tax rates include 5%
       const rates = taxBreakdown.map(slab => slab.slabPercentage);
-      expect(rates).not.toContain(5);
-      expect(rates).toEqual([0, 10, 15, 20, 25, 30]);
+      expect(rates).toContain(5);
+      expect(rates).toEqual([0, 5, 10, 15, 20, 25]);
     });
 
-    test('should show higher tax-free threshold for 2025-26', () => {
+    test('should show tax-free threshold for 2025-26', () => {
       store.commit('updateTaxpayerProfile', {
         category: 'general',
         age: 30,
@@ -119,7 +119,7 @@ describe('Calculation-2025 Component', () => {
       });
 
       const threshold = wrapper.vm.taxFreeThreshold;
-      expect(threshold).toBe(375000); // 25K higher than 2024-25
+      expect(threshold).toBe(350000); // Same as 2024-25 per NBR official
     });
 
     test('should apply unified minimum tax of 5000', () => {
@@ -161,7 +161,7 @@ describe('Calculation-2025 Component', () => {
       });
 
       const threshold = wrapper.vm.taxFreeThreshold;
-      expect(threshold).toBe(425000); // Female threshold for 2025-26
+      expect(threshold).toBe(400000); // Female threshold for 2025-26
     });
 
     test('should calculate correctly for disabled person', () => {
@@ -178,7 +178,7 @@ describe('Calculation-2025 Component', () => {
       });
 
       const threshold = wrapper.vm.taxFreeThreshold;
-      expect(threshold).toBe(500000); // Disabled threshold for 2025-26
+      expect(threshold).toBe(475000); // Disabled threshold for 2025-26
     });
 
     test('should calculate correctly for freedom fighter', () => {
@@ -195,7 +195,7 @@ describe('Calculation-2025 Component', () => {
       });
 
       const threshold = wrapper.vm.taxFreeThreshold;
-      expect(threshold).toBe(525000); // Freedom fighter threshold for 2025-26
+      expect(threshold).toBe(500000); // Freedom fighter threshold for 2025-26
     });
 
     test('should calculate correctly for third gender', () => {
@@ -212,7 +212,7 @@ describe('Calculation-2025 Component', () => {
       });
 
       const threshold = wrapper.vm.taxFreeThreshold;
-      expect(threshold).toBe(500000); // Third gender threshold for 2025-26
+      expect(threshold).toBe(475000); // Third gender threshold for 2025-26
     });
 
     test('should auto-detect senior citizen', () => {
@@ -229,7 +229,7 @@ describe('Calculation-2025 Component', () => {
       });
 
       const threshold = wrapper.vm.taxFreeThreshold;
-      expect(threshold).toBe(425000); // Senior threshold for 2025-26
+      expect(threshold).toBe(400000); // Senior threshold for 2025-26
     });
   });
 
@@ -258,13 +258,13 @@ describe('Calculation-2025 Component', () => {
       expect(totalTax).toBe(minimumTax); // Should apply minimum tax
     });
 
-    test('should calculate correct tax for income in first bracket (10%)', () => {
+    test('should calculate correct tax for income in first bracket (5%)', () => {
       store.commit('updateTaxpayerProfile', {
         category: 'general',
         age: 30,
         location: 'dhaka'
       });
-      
+
       store.commit('changeSubsequentSalaries', { index: 0, value: 40000 }); // 480K annually
 
       wrapper = mount(Calculation2025, {
@@ -274,10 +274,10 @@ describe('Calculation-2025 Component', () => {
       });
 
       const taxBreakdown = wrapper.vm.taxBreakdown;
-      
-      expect(taxBreakdown[0].slabCut).toBe(0); // No tax on first 375K
-      expect(taxBreakdown[1].slabCut).toBeGreaterThan(0); // Tax on excess at 10%
-      expect(taxBreakdown[1].slabPercentage).toBe(10); // First taxable bracket is 10%
+
+      expect(taxBreakdown[0].slabCut).toBe(0); // No tax on first 350K
+      expect(taxBreakdown[1].slabCut).toBeGreaterThan(0); // Tax on excess at 5%
+      expect(taxBreakdown[1].slabPercentage).toBe(5); // First taxable bracket is 5%
     });
 
     test('should apply minimum tax when calculated tax is lower', () => {
@@ -546,8 +546,8 @@ describe('Calculation-2025 Component', () => {
         age: 30,
         location: 'dhaka'
       });
-      
-      store.commit('changeSubsequentSalaries', { index: 0, value: 31250 }); // Exactly 375K annually
+
+      store.commit('changeSubsequentSalaries', { index: 0, value: 29167 }); // Exactly 350K annually
 
       wrapper = mount(Calculation2025, {
         global: {
@@ -558,7 +558,7 @@ describe('Calculation-2025 Component', () => {
       const taxBreakdown = wrapper.vm.taxBreakdown;
       const totalTax = wrapper.vm.totalTax;
       const minimumTax = wrapper.vm.minimumTaxAmount;
-      
+
       expect(taxBreakdown[0].slabCut).toBe(0);
       expect(totalTax).toBe(minimumTax); // Should apply minimum tax
     });
@@ -569,7 +569,7 @@ describe('Calculation-2025 Component', () => {
         age: 30,
         location: 'dhaka'
       });
-      
+
       store.commit('changeSubsequentSalaries', { index: 0, value: 500000 }); // 6M annually
 
       wrapper = mount(Calculation2025, {
@@ -580,8 +580,8 @@ describe('Calculation-2025 Component', () => {
 
       const taxBreakdown = wrapper.vm.taxBreakdown;
       const totalTax = wrapper.vm.totalTax;
-      
-      expect(taxBreakdown).toHaveLength(6);
+
+      expect(taxBreakdown).toHaveLength(7);
       expect(taxBreakdown[5].slabCut).toBeGreaterThan(0); // Highest slab should have tax
       expect(totalTax).toBeGreaterThan(100000); // Substantial tax amount
     });
@@ -592,7 +592,7 @@ describe('Calculation-2025 Component', () => {
         age: 30,
         location: 'dhaka'
       });
-      
+
       store.commit('changeSubsequentSalaries', { index: 0, value: 40000 });
 
       wrapper = mount(Calculation2025, {
@@ -602,16 +602,16 @@ describe('Calculation-2025 Component', () => {
       });
 
       const initialThreshold = wrapper.vm.taxFreeThreshold;
-      expect(initialThreshold).toBe(375000);
-      
+      expect(initialThreshold).toBe(350000);
+
       store.commit('updateTaxpayerProfile', {
         category: 'disabled',
         age: 30,
         location: 'dhaka'
       });
 
       const newThreshold = wrapper.vm.taxFreeThreshold;
-      expect(newThreshold).toBe(500000);
+      expect(newThreshold).toBe(475000);
     });
   });