Sigma Useful Tax Links

IRS Tax Links:

Internal Revenue Service

IRS Phone Numbers

Where to File Tax Returns

Local IRS Offices

Form 8822 – Change of Address

IRS Record Retention

IRS Payment Options:

IRS – E-Payment Options

EFTPS – Electronic Federal Tax Payment System

IRS Payment Plan/Installment Agreement

Find Out How Much You Owe IRS


Tax ID Numbers:

Taxpayer Identification Number (ITIN)

Form W-7

Tax Rates & Withholdings:

Federal Withholding Tax Calculator

State Individual Income Tax Rates

State Sales Tax Rates

2019 Tax Rates

Foreigners in US:

Tax Treaties

Pub. 519 – U.S. Tax Guide for Aliens

Foreign Students and Scholars

Liability for Social Security/Medicare Taxes

Refund of Social Security Taxes Withheld in Error

Withholding Rates

Visa Types

Maryland State Tax Links:

Comptroller of Maryland – Information for Business Taxpayers
Charter Business Services

Mayland –Payment Options

Maryland Phone Numbers

Maryland Individual Online Services

Maryland Business Online Services

Maryland Tax Calculators


Other Links:

Currency Converter

Domestic Per Diem Rates

Foreign Per Diem Rates

State Reciprocal Tax Agreements

Tax Research & Links:

Tax Topics

U.S. Tax Court

Americans Abroad:

Currency Converter

Pub. 54 – Tax Guide for Americans Abroad

Annual Foreign Exchange Rates

Treasury Exchanges Rates

International Social Security Agreements

International IRS Offices


State Government Websites

Visit the state websites below and find information on doing business in the state, taxation, links for employers, and more.

·         Alabama

·         Alaska

·         Arizona

·         Arkansas

·         California

·         Colorado

·         Connecticut

·         Delaware

·         District of Columbia

·         Florida

·         Georgia

·         Hawaii

·         Idaho

·         Illinois

·         Indiana

·         Iowa

·         Kansas

·         Kentucky

·         Louisiana

·         Maine

·         Maryland

·         Massachusetts

·         Michigan

·         Minnesota

·         Mississippi

·         Missouri

·         Montana

·         Nebraska

·         Nevada

·         New Hampshire

·         New Jersey

·         New Mexico

·         New York

·         North Carolina

·         North Dakota

·         Ohio

·         Oklahoma

·         Oregon

·         Pennsylvania

·         Rhode Island

·         South Carolina

·         South Dakota

·         Tennessee

·         Texas

·         Utah

·         Vermont

·         Virginia

·         Washington 

·         West Virginia

·         Wisconsin

·         Wyoming