Did you get any refund from the tax office this time or paid some tax by the 2nd of June?
A lot of expats are missing this filing since they thought that his or her employer did it, or already paid enough tax for 3.3% of their monthly income, or simply didn't know how to do it.
I found that a lot of my expat friends talked to me that just didn't file for the last 3 or 5 years and just run away when he got a notice from the NTS(Korean IRS) enforcing to pay some millions global income tax. I'll explain this taxation for all of teachers and professors in Korea.
If you're employed by a school or Hagwon, and no other income(3.3% withholding tax-income), your employer need to take care all about your tax and very simple. But as I insist before, still you need to keep those tax receipts(근로소득원천징수영수증) which is issued by your employer by the February once a year and also need to keep your pay slip to verify your deduction items from your salary by your employer. This is because some of your employer deduct your income tax and 4 major insurances from your salary and do not pay it properly to the concerned parties and make you a fool thereafter. If you had an employer and work for extra money and paid 3.3% of tax, you have to file a tax return for the global income tax by the end of following year May including your last year salary and 3.3% income you earned. Even I found that some of my clients used to pay 3.3% tax but no records in the tax office and can't claim to anybody since there is no receipts or evidence.
No matter what, you need to ask the pay slip which is clearly stated for your income and withholding tax and other deductible items(even retirement allowances, 4 major insurances or whatsoever) for your tax filing. I used to review those sources of income(salary or other 3.3% income, or retirement allowance) for my clients and file it correctly for the last 3 to 5 years if necessary. For your information you can file a tax return for the last 3 years(2011~2013), and some times a kind tax officer allow us to correct some deduct if it's wrongly stated on the tax file for the 5 years ago. It may depends on your income amount but you can get refund if you filed, how did you know you need to pay more or get refund? Please ask me through an email, it's that simple if you knew my email address, firstname.lastname@example.org!