Started a small side hustle, do I need to declare it and tell my employer?

Two separate issues, tax and employment. Tax: yes, freelance income is taxable and you must declare it to IRAS as trade or self-employed income when you file, even if it's a few hundred a month. Keep records of what you earn and your related expenses (software, equipment) because you're taxed on net profit and can deduct legitimate costs. It's not scary, you just add it in your annual filing. Employment: check your contract for a moonlighting or conflict-of-interest clause, many SG employers require you to declare outside work or forbid competing work. As long as your freelance design isn't competing with your employer, isn't done on company time or equipment, and doesn't breach your contract, you're usually fine, but read the clause. If in doubt, a quiet declaration to HR protects you. The two things people trip on: not declaring the income, and using their work laptop for side gigs. Avoid both.