Introduction: Why Accurate Salary Calculation Matters
Salary calculation is one of the most critical processes in any organization. Even small errors can impact employee trust, labor compliance, accounting accuracy, and tax reporting.
This guide covers:
The 30-day salary calculation rule
Prorated salary for new joiners and resignations
Overtime calculation
Net salary after Social Security and tax deductions
How to Convert Monthly Salary to Daily Rate
The 30-Day Rule (Featured Snippet Answer)
Daily Salary = Monthly Salary ÷ 30
The 30-day standard ensures consistent payroll calculation throughout the year.
Even if a month has 28 or 31 days, the 30-day rule is commonly used for salaried employees in Thailand.
Organizations should apply this method consistently.
Should February (28 Days) Be Divided by 28 or 30?
In practice, salaried employees are typically calculated using the 30-day standard.
Why the 30-Day Rule Is Commonly Used
Maintains payroll consistency
Prevents monthly fluctuation
Aligns with overtime and prorated calculations
Salary Calculation for Mid-Month Joiners
Formula
Daily Rate × Eligible Working Days
Example
Monthly Salary: 30,000 THB
30,000 ÷ 30 = 1,000 THB/day
Start Date: 20th (11 eligible days)
1,000 × 11 = 11,000 THB
Salary Calculation for Mid-Month Resignation
Formula
Daily Rate × Actual Working Days
Example
30,000 THB monthly
Resigned on the 5th
1,000 × 5 = 5,000 THB
Additional payable items such as accrued leave should also be reviewed.
Salary Deduction for Unpaid Leave or Absence
Formula
Monthly Salary – (Daily Rate × Unpaid Days)
Example
Monthly Salary: 18,000 THB
18,000 ÷ 30 = 600 THB/day
1 day unpaid leave
18,000 – 600 = 17,400 THB
Overtime Calculation from Monthly Salary
Hourly Rate Formula
Hourly Rate = Monthly Salary ÷ 30 ÷ 8
Overtime Formula (Normal Working Day)
Overtime Pay = Hourly Rate × 1.5 × OT Hours
Example
Monthly Salary: 30,000 THB
30,000 ÷ 30 = 1,000
1,000 ÷ 8 = 125 THB/hour
2 hours OT
125 × 1.5 × 2 = 375 THB
Overtime rates may vary for public holidays and rest days under Thai labor law.
Working Hours Under Thai Labor Law
Generally:
Maximum 8 hours per day
Maximum 48 hours per week
Hours beyond normal working schedule are considered overtime.
Gross Salary vs Net Salary
Gross Salary
Salary before any deductions.
Net Salary
Take-home pay after deductions such as:
Social Security
Withholding tax
Provident Fund (if applicable)
Net Salary After Social Security Deduction
Standard Contribution
5% of wages (subject to legal ceiling)
Example
Monthly Salary: 30,000 THB
Maximum Social Security deduction: 875 THB (based on current ceiling)
Net Salary After Income Tax Deduction
Income tax depends on:
Annual income
Personal allowances
Marital status
Example:
30,000 THB/month = 360,000 THB/year
Tax is calculated using Thailand’s progressive tax rates.
Complete Payroll Scenario (Full Case Example)
Employee:
- 30,000 THB monthly
- Joined on the 20th
- 2 hours overtime
- 1 unpaid leave day
Calculation Steps
1️⃣ Prorated salary = 11,000
2️⃣ Deduct unpaid leave = –1,000
3️⃣ Add OT = +375
4️⃣ Deduct Social Security
5️⃣ Deduct withholding tax
This illustrates how payroll integrates multiple components in one pay cycle.
Salary Calculation Summary Table
Case | Formula | Example (30,000 THB) |
Daily Rate | Salary ÷ 30 | 1,000 THB |
Join mid-month | 1,000 × 11 | 11,000 THB |
Resign day 5 | 1,000 × 5 | 5,000 THB |
1 unpaid day | 30,000 – 1,000 | 29,000 THB |
2 hrs OT | 125 × 1.5 × 2 | 375 THB |
How to Avoid Payroll Errors
Apply consistent calculation standards
Clearly define eligible working days
Separate paid and unpaid leave types
Verify attendance before payroll cutoff
Use integrated Payroll and Time Attendance systems
FAQ
Should salary always be divided by 30?
Common practice applies the 30-day rule for salaried employees.
Is the 30-day rule legally mandatory?
Organizations may define their own policy but should apply it consistently and fairly.
How much net salary will 30,000 THB receive?
It depends on Social Security and income tax deductions.
Disclaimer
This article is for general informational purposes only and does not constitute legal advice. Organizations should verify current regulations before implementation.
https://legal.labour.go.th/attachments/article/823/56_00683.pdf
https://legal.labour.go.th/attachments/article/823/66_00002.pdf