Quarterly taxes are due 4 times a year. They don’t follow the standard calendar quarter schedule though. The estimated tax on your net income from:
January to March is due April 15;
April to May is due June 15;
June-August is due Sept 15;
September-December is due Jan 15.
Key distinction is that the tax is due on your net income, not gross, so you need to know your expenses for the same time period. Also, you will be paying federal income tax, FICA (social security and Medicare) tax, and your State and Local taxes (SALT) on these dates, so you need to calculate all 3 separately. Namu does this for you automatically and we can talk you through all this.