13th month pay in belgium

It will depend on your specific contract, but typically, the 13th month accrues to you in the current year, therefore, if you leave today, you will get 9/12th of the 13th month.  (You should also get 9/12th of the 0.89 months pecule you would normally be paid NEXT year in June)  Remember however that these payments will be taxed at your highest marginal tax rate, and have the full ONSS deductions made, so you'll probably end up with less than half.  Finally, if you are leaving the country, you need to file a tax return, as you'll probably be due a refund.  If you're transferring to another job in Belgium you won't get any paid holiday next year.