diff --git a/src/app.module.ts b/src/app.module.ts
index 1a4c3a7..b9c689c 100644
--- a/src/app.module.ts
+++ b/src/app.module.ts
@@ -17,6 +17,7 @@ import { PayperiodsModule } from './modules/pay-periods/pay-periods.module';
 import { ScheduleModule } from '@nestjs/schedule';
 import { ArchivalModule } from './modules/archival/archival.module';
 import { BankCodesModule } from './modules/bank-codes/bank-codes.module';
+import { OvertimeService } from './business-logic/overtime.service';
 
 @Module({
   imports: [
@@ -37,6 +38,6 @@ import { BankCodesModule } from './modules/bank-codes/bank-codes.module';
       PayperiodsModule,
     ],
   controllers: [AppController, HealthController],
-  providers: [AppService],
+  providers: [AppService, OvertimeService],
 })
 export class AppModule {}
diff --git a/src/business-logic/holiday.service.ts b/src/business-logic/holiday.service.ts
new file mode 100644
index 0000000..e69de29
diff --git a/src/business-logic/overtime.service.ts b/src/business-logic/overtime.service.ts
new file mode 100644
index 0000000..b99122b
--- /dev/null
+++ b/src/business-logic/overtime.service.ts
@@ -0,0 +1,82 @@
+import { Injectable, Logger } from '@nestjs/common';
+import { PrismaService } from 'src/prisma/prisma.service';
+
+@Injectable()
+export class OvertimeService {
+    
+    private logger = new Logger(OvertimeService.name);
+    private dailyMax = 8; // maximum for regular hours per day
+    private weeklyMax = 40; //maximum for regular hours per week
+
+    constructor(private prisma: PrismaService) {}
+
+    // calculate decimal hours rounded to nearest 5 min
+    computedHours(start: Date, end: Date): number {
+        const durationMs = end.getTime() - start.getTime();
+        const totalMinutes = durationMs / 60000;
+
+        //rounded to 5 min
+        const rounded = Math.round(totalMinutes / 5) * 5;
+        const hours = rounded / 60;
+        this.logger.debug(`computedHours: raw=${totalMinutes.toFixed(1)}min rounded = ${rounded}min (${hours.toFixed(2)}h)`);
+        return hours;
+    }
+
+    //calculate Daily overtime
+    getDailyOvertimeHours(start: Date, end: Date): number {
+        const hours = this.computedHours(start, end);
+        const overtime = Math.max(0, hours - this.dailyMax);
+        this.logger.debug(`getDailyOvertimeHours : ${overtime.toFixed(2)}h (threshold ${this.dailyMax})`);
+        return overtime;
+    }
+
+    //sets first day of the week to be sunday
+    private getWeekStart(date:Date): Date {
+        const d = new Date(date);
+        const day = d.getDay(); // return sunday = 0, monday = 1, etc
+        d.setDate(d.getDate() - day);
+        d.setHours(0,0,0,0,); // puts start of the week at sunday morning at 00:00
+        return d;
+    }
+
+    //sets last day of the week to be saturday
+    private getWeekEnd(startDate:Date): Date {
+        const d = new Date(startDate);
+        d.setDate(d.getDate() +6); //sets last day to be saturday
+        d.setHours(23,59,59,999); //puts end of the week at saturday night at 00:00 minus 1ms
+        return d;
+    }
+
+    //calculate Weekly overtime
+    async getWeeklyOvertimeHours(employeeId: number, refDate: Date): Promise<number> {
+        const weekStart = this.getWeekStart(refDate);
+        const weekEnd = this.getWeekEnd(weekStart);
+
+        //fetches all shifts containing hours
+        const shifts = await this.prisma.shifts.findMany({
+            where: { timesheet: { employee_id: employeeId, shift: { 
+                every: {date: { gte: weekStart, lte: weekEnd } }
+                },
+             },
+         },
+         select: { start_time: true, end_time: true },
+        });
+
+        //calculate total hours of those shifts minus weekly Max to find total overtime hours
+        const total = shifts.map(shift => this.computedHours(shift.start_time, shift.end_time))
+                                              .reduce((sum, hours)=> sum+hours, 0);
+        const overtime = Math.max(0, total - this.weeklyMax);
+
+        this.logger.debug(`weekly total = ${total.toFixed(2)}h, weekly Overtime= ${overtime.toFixed(2)}h`);
+        return overtime;
+    }
+
+    //apply modifier to overtime hours
+    calculateOvertimePay(overtimeHours: number, modifier: number): number {
+        const pay = overtimeHours * modifier;
+        this.logger.debug(`Overtime payable hours = ${pay.toFixed(2)} (hours ${overtimeHours}, modifier ${modifier})`);
+
+        return pay;
+    }
+
+}
diff --git a/src/business-logic/sick-leave.service.ts b/src/business-logic/sick-leave.service.ts
new file mode 100644
index 0000000..e69de29
diff --git a/src/business-logic/vacation.service.ts b/src/business-logic/vacation.service.ts
new file mode 100644
index 0000000..e69de29
diff --git a/src/modules/timesheets/services/timesheets.service.ts b/src/modules/timesheets/services/timesheets.service.ts
index c8fcff3..4cc519d 100644
--- a/src/modules/timesheets/services/timesheets.service.ts
+++ b/src/modules/timesheets/services/timesheets.service.ts
@@ -3,51 +3,80 @@ import { PrismaService } from 'src/prisma/prisma.service';
 import { CreateTimesheetDto } from '../dtos/create-timesheet.dto';
 import { Timesheets, TimesheetsArchive } from '@prisma/client';
 import { UpdateTimesheetDto } from '../dtos/update-timesheet.dto';
+import { OvertimeService } from 'src/business-logic/overtime.service';
 
 @Injectable()
 export class TimesheetsService {
-    constructor(private readonly prisma: PrismaService) {}
+    constructor(
+        private readonly prisma: PrismaService,
+        private readonly overtime: OvertimeService,
+    ) {}
 
     async create(dto : CreateTimesheetDto): Promise<Timesheets> {
         const { employee_id, is_approved } = dto;
         return this.prisma.timesheets.create({
-            data: {
-                employee_id,
-                is_approved: is_approved ?? false,
-            },
+            data: { employee_id, is_approved: is_approved ?? false },
             include: {
-                employee: {
-                    include: { user: true }
+                employee: { include: { user: true }
                 },
             },
         });
     }
 
-    findAll(): Promise<Timesheets[]> {
-        return this.prisma.timesheets.findMany({
-            include: {
-                employee: {
-                    include: { user: true },
-                },
+    async findAll(): Promise<any[]> {
+        const list = await this.prisma.timesheets.findMany({
+            include: { 
+                shift: { include: { bank_code: true } },
+              expense: { include: { bank_code: true } },
+             employee: { include: { user : true } },
             },
         });
+
+        return Promise.all(
+            list.map(async timesheet => {
+                const detailedShifts = timesheet.shift.map(s => {
+                    const hours         = this.overtime.computedHours(s.start_time, s.end_time);
+                    const regularHours  = Math.min(8, hours);
+                    const dailyOvertime = this.overtime.getDailyOvertimeHours(s.start_time, s.end_time);
+                    const payRegular    = regularHours * s.bank_code.modifier;
+                    const payOvertime   = this.overtime.calculateOvertimePay(dailyOvertime, s.bank_code.modifier);
+                    return { ...s, hours, payRegular, payOvertime };
+                });
+                const weeklyOvertimeHours = detailedShifts.length
+                            ? await this.overtime.getWeeklyOvertimeHours(
+                                                timesheet.employee_id,
+                                                timesheet.shift[0].date): 0;
+                return { ...timesheet, shift: detailedShifts, weeklyOvertimeHours };
+            })
+        ); 
     }
 
-    async findOne(id: number): Promise<Timesheets> {
-        const record = await this.prisma.timesheets.findUnique({
+    async findOne(id: number): Promise<any> {
+        const timesheet = await this.prisma.timesheets.findUnique({
             where: { id },
-            include: {
-                employee: {
-                    include: {
-                        user:true
-                    }
-                },
-            },
+          include: {
+            shift: { include: { bank_code: true } },
+          expense: { include: { bank_code: true } },
+         employee: { include: { user: true } },
+          },
         });
-        if(!record) {
+        if(!timesheet) {
             throw new NotFoundException(`Timesheet #${id} not found`);
         }
-        return record;
+
+        const detailedShifts = timesheet.shift.map( s => {
+                const hours         = this.overtime.computedHours(s.start_time, s.end_time);
+                const regularHours  = Math.min(8, hours);
+                const dailyOvertime = this.overtime.getDailyOvertimeHours(s.start_time, s.end_time);
+                const payRegular    = regularHours * s.bank_code.modifier;
+                const payOvertime   = this.overtime.calculateOvertimePay(dailyOvertime, s.bank_code.modifier);
+                return { ...s, hours, payRegular, payOvertime };
+            });
+            const weeklyOvertimeHours = detailedShifts.length
+                        ? await this.overtime.getWeeklyOvertimeHours(
+                                            timesheet.employee_id,
+                                            timesheet.shift[0].date): 0;
+            return { ...timesheet, shift: detailedShifts, weeklyOvertimeHours };
     }
 
     async update(id: number, dto:UpdateTimesheetDto): Promise<Timesheets> {
@@ -59,19 +88,14 @@ export class TimesheetsService {
                 ...(employee_id !== undefined && { employee_id }),
                 ...(is_approved !== undefined && { is_approved }),
             },
-            include: {
-                employee: {
-                    include: { user: true }
-                },
+            include: { employee: { include: { user: true } },
             },
         });
     }
 
     async remove(id: number): Promise<Timesheets> {
         await this.findOne(id);
-        return this.prisma.timesheets.delete({
-            where: { id },
-        });
+        return this.prisma.timesheets.delete({ where: { id } });
     }
 
 
@@ -85,8 +109,7 @@ export class TimesheetsService {
         await this.prisma.$transaction(async transaction => {
             //fetches all timesheets to cutoff
             const oldSheets = await transaction.timesheets.findMany({
-                where: { shift: { every: { date: { lt: cutoff } },
-                    },
+                where: { shift: { every: { date: { lt: cutoff } } },
                 },
                 select: {
                     id: true,
@@ -106,14 +129,10 @@ export class TimesheetsService {
             }));
 
             //copying data from timesheets table to archive table
-            await transaction.timesheetsArchive.createMany({
-                data: archiveDate,
-            });
+            await transaction.timesheetsArchive.createMany({ data: archiveDate });
 
             //removing data from timesheets table
-            await transaction.timesheets.deleteMany({
-                where: { id: { in: oldSheets.map(s => s.id) } },
-            });
+            await transaction.timesheets.deleteMany({ where: { id: { in: oldSheets.map(s => s.id) } } });
         });
     }