If you earn your income as self employed or as a contractor, then you would owe taxes anytime you make more than $400 per year. Income earned through self employment or contractor work is not taxed by an "employer", so you are responsible for reporting your income and paying your own taxes on that income including social security and medicare taxes.
If you work a job in which you have filled out a W-4 form and will be getting a W-2 form at the end of the year, then your refund is based on a combination of your total income and how you filled out your W-4 for what should be withheld. Social Security tax and Medicare taxes are NOT REFUNDED. Federal income tax is refunded IF YOU OVERPAID. For a single person, you can make up to $12,200 before you owe federal income tax. So, if your income is below that amount and you had federal taxes withheld, you would get a refund of ALL the federal taxes that were withheld. If you make more than $12,200 then your refund is based on the difference between what you owe and what you paid. If you paid too much in, then you get a refund of the difference. If you didn't pay enough in, then you owe more.
Remember, a refund is just YOUR MONEY that you over paid based on how you filled out your W-4 when you started the job. If you want to guarantee a refund - then over pay by more money. But then you are just giving the government an interest free loan of YOUR MONEY. (There is a line on the W-4 form that gives you a chance to have an additional amount withheld. I knew someone who was so paranoid about getting a refund that they always had an additional $20 withheld from each paycheck. Of course, they always had a good refund - but it was just their money that they were getting back)
Basically - if you put the correct information on your W-4 form, you can always get a refund no matter how much money you make. You just need to make sure that you are having enough money applied to taxes to over pay your tax liability.
On a W-4 filing as single with 0 allowances almost always creates a refund. (but it is still just your money that you overpaid. The government is only giving you back your money)
Filing as single with 1 allowance usually creates a small refund.
Filing as single with 2 allowances MIGHT cause you to need to pay a little more taxes.
If you work more than one job, then it is best to claim all jobs as single with 0 allowances.
You might know some people who are getting large refunds based on TAX CREDITS for things like children or low income. If you are single and between the ages of 25 to 65 - then you MIGHT qualify for a TAX CREDIT for earned income. To qualify, your income would need to be below $15,270 for the year. A tax credit is not your money being refunded. It is a credit given for certain tax situations if the person filing qualifies for it.