Your contribution limit depends on your age and earned income. The maximum amount allowed by law that you can contribute to your IRA in 2018 is $5,500 if you are under the age of 50 and $6,500 if you are 50 or older. For 2019, this limit increases to $6,000 if you are under the age of 50 and $7,000 if you are 50 or older.
If your earned income is less than these amounts, the maximum allowable contribution is 100% of your earned income.
There may also be some income limitations to maximum contributions. Check here for more information on maximum contributions: IRS Calculations or contact a tax professional.