From the Office of Tax and Revenue website:
The housing market in the District of Columbia has caused a surge in the assessed value of residential real property. In an effort to limit the increase of real property taxes for homeowners, eligible homeowners will be provided an Assessment Cap Credit.
The Assessment Cap currently provides that a property may not be taxed on more than a 10 percent increase in the property’s assessed value each year. This credit does not reduce the assessed value of your property on the tax roll or the assessment notice, but it will appear as an automatic credit against your real property tax bill.
For more information, property owners may call the Customer Service Center at (202) 727-4TAX (727-4829).
If you have been denied the Assessment Cap Credit and you believe that you are eligible, please contact the Homestead Unit, PO Box 176, Washington, DC 20044 or call Customer Service at (202) 727-4TAX.