Corporate tax filing in Singapore is a critical responsibility for all businesses. Yet, many companies — especially startups and SMEs — make common errors that can lead to penalties, audits, or missed tax benefits. Whether you’re filing Form C, Form C-S, or dealing with IRAS queries, understanding what to avoid can save time, money, and stress.

In this article, we break down the top 5 corporate tax mistakes Singapore companies make and share practical tips to help you stay compliant and confident.

Singapore companies are required to file their Estimated Chargeable Income (ECI) within 3 months of the financial year end, and their Corporate Income Tax return (Form C or Form C-S) by 30 November each year.

Why it happens:
• Lack of awareness of the deadlines
• Incomplete accounting records
• Miscommunication between finance and tax teams

How to avoid it:
• Set automated reminders based on your company’s financial year end
• Engage a reliable tax service provider to track and file on time
• Prepare your accounts early — don’t wait until year-end

Many companies are eligible to file the simplified Form C-S, but either don’t realise it or choose the wrong form.

Form C-S is for qualifying companies with:
• Revenue ≤ S$5 million
• No claim of carry-back losses or group relief
• Income taxable at prevailing corporate tax rate

Why it matters: Filing the wrong form can lead to unnecessary complexity or even rejection.

How to avoid it:
• Check your eligibility annually
• Consult your tax advisor if you’re unsure
• Keep financial records structured for easy classification

Incorrectly reporting taxable income, or over-claiming deductions (e.g. expenses not wholly incurred for business), is a common trigger for IRAS audits.

Common issues:
• Misclassifying capital vs revenue expenses
• Claiming private or non-business-related costs
• Failing to substantiate expense claims with proper documentation

How to avoid it:
• Maintain clear, audit-ready documentation
• Understand IRAS guidelines on allowable deductions
• Review returns with a tax specialist before submission

IRAS may raise queries on discrepancies or trends that appear unusual. Many companies scramble to respond due to lack of preparation.

Why it happens:
• Poor recordkeeping
• No centralised filing system for receipts and contracts
• Tax submissions done without internal review

How to avoid it:
• Keep records for at least 5 years as required by IRAS
• Store documents in a digital, organised format
• Have a tax advisor familiar with handling IRAS correspondence

Corporate tax filing isn’t just about compliance. It’s also an opportunity to optimise your tax position. Many companies miss this by taking a passive approach.

Examples of missed opportunities:
• Not utilising tax exemptions for new startups
• Overlooking productivity and innovation credit (PIC) or other available schemes
• Not considering group relief or unutilised losses

How to avoid it:
• Work with a tax consultant to review your structure annually
• Plan ahead — tax-saving strategies must be implemented before year-end
• Stay updated on new IRAS tax incentives and changes

Corporate tax filing in Singapore doesn’t have to be stressful. With the right systems and professional support, you can stay compliant, reduce risk, and even improve your bottom line through effective tax planning.

At Profectant, we support over 800 companies with their corporate tax needs — from ECI filing to tax advisory and IRAS audit support. If you’d like to review your tax processes or get help with filing, our team is here to assist.

Need help with your Singapore corporate tax filing? Reach out to us for a no-obligation consultation.