For 2018, the maximum total amount you and/or your employer can contribute to your HSA account is $3,450 for an individual plan, or $6,900 for a family plan. This is the sum of both your contribution and your employer's.
If you're 55 or older, you're also allowed to contribute up to an additional $1,000 for a maximum of $4,450 (individual) or $7,900 (family).
The following TurboTax FAQ further explains HSA contribution limits. https://ttlc.intuit.com/replies/4788059