How to Calculate Incomplete Month Salary for Singapore Employees

Many companies default to simplistic pro-rata or calendar-day calculations when paying partial months. This can risk underpayment, disputes, or non-compliance with MOM rules. 

The Ministry of Manpower (MOM) in Singapore understands how the proration of payment of salaries should be in an incomplete month. Payroll managers, the HR leaders, and the business owners should be aware of these regulations in order to give fair and correct pay. 

This guide defines an incomplete month salary, the formula to compute this using the MOM, the common pitfalls to avoid, and how to make the process easier.

Understanding Incomplete Month Salary in Singapore

Incomplete month salary refers to the prorated salary an employee receives when they do not work the full calendar month. In Singapore, this typically occurs when an employee:

• Joins mid-month or after the 1st: g. a new hire starting on the 15th.
• Leaves employment mid-month: e.g., resignations or terminations before month-end.
• Takes unpaid leave during the month: extended no-pay leave days reduce paid days.
• Goes for reservist (NS) training during the month: considered a period of unpaid absence.

MOM defines an “incomplete month of work” as any month where the employee starts after the first day, leaves before the last day, or has one or more no-pay leave or reservist days.

In such cases, the employee should only be paid for the days actually worked (including paid leave and holidays), rather than the full monthly salary. Prorating the salary ensures fair compensation for time worked while keeping employers compliant with Singapore’s Employment Act.

Key Definitions & Distinctions for Incomplete Month Salary

Before jumping into formulas for incomplete month salary, it helps to clarify a few key terms MOM uses when you calculate incomplete month pay. Getting these right makes all the difference between compliance and confusion:

Gross vs basic

The monthly gross rate of pay is the total amount an employee earns in a full month, including their basic daily salary and any fixed allowances stated in the contract. It excludes variable components like overtime, bonuses, Annual Wage Supplement (AWS), or reimbursements. When you calculate incomplete month salary, always use the gross rate of pay, not just basic pay. The MOM incomplete month formula is based on this gross figure because it reflects an employee’s regular, fixed earnings.

Working days vs calendar days

According to the MOM working days guidelines, prorated salary is based on working days, not total calendar days. Working days are the days the employee is scheduled to work, usually Monday to Friday, and include public holidays that fall on those days. Weekends and rest days don’t count. 

Using 30 or 31 days as the divisor might seem easier, but it’s not compliant and often leads to underpayment. Always check how many working days are in that specific month, and for your company’s workweek pattern.

What is excluded

Certain components are not included when prorating salary. These include overtime pay, bonuses, Annual Wage Supplement (AWS), commissions (unless fixed), and allowances that vary monthly. Unpaid leave days, no-pay absences, or days after resignation are also excluded when counting “days actually worked.” For example, if an employee takes two days of unpaid leave, those two days are deducted from their paid working days in the incomplete month salary calculation.

Public holiday treatment

For monthly-rated employees, if a public holiday falls on a normal working day, it’s treated as a paid day off. That holiday is included in both the total working days and the employee’s days worked as long as they were employed on that date. If the person joins after the holiday or leaves before it, that day isn’t paid. Always double-check public holidays when you calculate incomplete month pay to avoid payroll errors.

Learn more: Singapore Public Holidays 2025

Calculating Incomplete Month Salary

When an employee joins in the middle of the month, leaves early, or takes unpaid leave, you will need to calculate an incomplete month salary. MOM provides a clear formula to ensure every case is handled fairly and consistently:

Incomplete month salary = (Monthly gross rate of pay ÷ Total number of working days in that month) × Number of days worked

This formula prorates salary based on the number of paid working days in that month and helps HR teams stay compliant with MOM’s incomplete month rules.

• Monthly gross rate of pay: The employee’s fixed monthly salary, including basic pay and any fixed allowances. It excludes variable pay like overtime, bonuses, AWS, or expense claims.
• Total number of working days in that month: The MOM working days divide the number of scheduled workdays for that month based on your company’s workweek. It excludes weekends and rest days but includes public holidays that fall on workdays. For instance, April 2025 has 22 working days for a standard Monday–Friday workweek. 
• Number of days worked: The paid days the employee actually worked or was on paid leave (annual leave, paid medical leave, or public holidays). Unpaid leave or days after resignation don’t count.

Relevant reading: How to Calculate Daily Salary in Singapore: A Step-By-Step Guide

Once you’ve confirmed these numbers, multiply them according to the formula to get the prorated or incomplete month salary.

Examples: How to Calculate Incomplete Month Salary

Let’s look at some examples to understand how to calculate incomplete month salary under the MOM guidelines in Singapore.

Daniel’s employment contract states a monthly gross salary of S$4,000. His company works Monday to Friday, following MOM’s official working days calendar.

Mid-month joiner

If Daniel joins the company on 15 April 2025, there are 22 total working days in April. He works 12 days (from 15–30 April, excluding weekends but including one paid public holiday).

Calculation:
S$4,000 ÷ 22 × 12 = S$2,181.82

His incomplete month salary for April is S$2,181.82.

Resignation or leaving early

If Daniel resigns and his last working day is 10 May 2025, there are 21 total working days in May. He works 9 days (1 to 10 May, including Labour Day as a paid public holiday).

Calculation:
S$4,000 ÷ 21 × 9 = S$1,714.29

His final salary covers all paid days before he leaves. Since Labour Day falls within his employment period, it counts as a paid day.

Unpaid leave within the month

In June, if Daniel takes five days of unpaid leave, and there are 20 total working days, he only works 15 days.

Calculation:
S$4,000 ÷ 20 × 15 = S$3,000.00

His incomplete month salary after deducting no-pay leave is S$3,000.00.

Reservist, NS, or training during the month

In July, Daniel attends two weeks of reservist training (10 working days). There are 23 total working days that month, so he works 13 days in total.

Calculation:
S$4,000 ÷ 23 × 13 = S$2,260.87

His employer pays only for the 13 days she worked. The 10 reservist days are covered under MINDEF’s make-up pay system, ensuring Daniel still receives his full income through both sources.

Read next: NSMen Make-Up Pay: A Guide for Singapore Businesses

Summary

These examples show how to calculate incomplete month salary in different situations — whether you are a new joiner, leaving early, taking unpaid leave, or attending training or reservist.

When working out an incomplete month, always check:

• The total MOM working days for that month.
• How many days did the employee actually work.
• Whether public holidays fall within the employment period.

You can use a salary calculator Singapore, gross income calculator, or paycheck calculator to verify your calculations.

Understanding how many working days are in a month and how many working days are in a year helps ensure your incomplete month salary calculations are accurate and compliant with MOM's incomplete month guidelines.

Why MOM’s formula matters

Using MOM’s incomplete month salary formula, which is based on working days instead of calendar days, helps employers stay compliant with Singapore’s employment laws and avoid salary disputes.

This formula ensures employees, like Daniel in our example, are fairly paid for every day they are entitled to, no matter how long they’ve worked in that month.

For small teams, it’s possible to use a manual gross income calculator or paycheck calculator to work out the numbers. However, as companies grow, automated payroll software becomes more efficient and reliable.

Payroll tools such as Omni automatically apply MOM’s incomplete month formula, sync with leave and attendance data, and generate accurate payslips. This saves time, reduces human error, and ensures every salary calculation remains compliant and audit-ready.

Common Mistakes When Calculating Incomplete Month Salary

Even with MOM’s formula, small errors can easily throw off your incomplete month salary calculations. Here are some of the most common mistakes HR teams should avoid.

• Using calendar days instead of working days: MOM’s formula uses working days, not calendar days. Including weekends or rest days in the divisor leads to underpayment. Always use the actual number of working days in that month. Refer to the MOM’s working-day table or a trusted salary calculator Singapore.
• Including overtime, bonuses, variable pay in proration incorrectly: Only the monthly gross rate of pay (basic salary plus fixed allowances) should be prorated. Over time, bonuses or variable commissions are excluded under MOM’s guidelines. Use only fixed contractual pay when you calculate an incomplete month's salary.
• Forgetting to subtract unpaid leave days: Unpaid leave days must be excluded from the “days worked” total. Leaving them results in overpayment and Central Provident Fund (CPF) errors. Ensure your leave and payroll systems are linked so unpaid days are automatically deducted.
• Miscounting public holidays: Public holidays that fall within employment should be counted as paid days. Excluding or double-counting them leads to inaccurate pay. Cross-check your payroll period against MOM’s public holiday list.
• Not reconciling with contractor/shift / part-time work patterns: Not all employees follow the same schedule. MOM’s working-day divisor differs for 5-day, 5.5-day, or 6-day workweeks. Apply the correct divisor based on each employee’s actual work pattern.
• Using a flat daily rate method that conflicts with the MOM prescription: Relying on a fixed daily rate (for example, dividing salary by 21.75 days) ignores monthly variations and conflicts with the MOM’s formula. Recalculate the divisor each month or use payroll software that adjusts automatically.

Tools & Calculators to Calculate Incomplete Month Salary

MOM’s incomplete month calculator is the easiest way to verify prorated pay. It applies the official MOM formula and requires only three inputs: the employee’s monthly salary, how many working days in a month, and the number of paid days worked. 

Once entered, it instantly provides the correct incomplete month salary figure, making it especially useful for spot checks or smaller teams handling payroll manually.

Several salary calculator Singapore tools also follow MOM’s guidelines and allow users to toggle between 5-day, 5.5-day, or 6-day workweeks. These tools are practical for quick, one-off calculations but aren’t designed to manage payroll on an ongoing basis.

The main limitation of these standalone calculators is that they work in isolation. Every entry must be done manually, and they don’t sync with other HR data, such as leave, attendance, or CPF contributions. This can quickly become time-consuming and prone to errors once you are processing salaries for multiple employees each month.

That’s where payroll software becomes a more efficient and reliable option than a basic paycheck calculator.

Automating Incomplete Month Salary Calculations with Omni

Modern payroll systems like Omni go beyond simple calculations to make incomplete month salary processing faster, more accurate, and fully compliant. Omni’s all-in-one HR platform connects payroll, time-off, attendance, and employee data in one place, helping HR teams save hours each month.

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With Omni, you can: 

• Automatically apply MOM’s working-day formula for incomplete month salary calculations.
• Sync attendance, leave, and public holiday data in real time.
• Adjust working-day counts based on workweek patterns.
• Calculate CPF and tax deductions accurately and in compliance with local regulations.
• Generate itemized, audit-ready payslips in seconds.
• Access full audit trails and automated reminders for transparency and compliance.
• Run localized, multi-country payroll across 190+ countries and 10+ languages.

By automating incomplete month salary calculations with Omni, HR teams can significantly reduce manual work, eliminate errors, and ensure every calculation is precise, compliant, and audit-ready. Book a demo with our team today and learn more.