IRS Tax Calendar for Businesses and Self-Employed

Firefox has some terribad font rendering engine, especially on Windows. Anyway it's 2019 and you should be using Chrome already...

It looks okay in FF 66.0.5 on Windows 7

The format and customizations are new. For ex, here's the 2012 version https://www.irs.com/articles/2012-tax-calendar

Take the time to add all of the important deadlines to your personal calendar. The days shift slightly year by year, so a repeating reminder didn't work for me. The last prepaid tax payment for 2019 is due on January 15, 2020 and any 1099 to contractors are due at the end of the month, so don't forget those as well. There's a couple of miscellaneous dates around there as well, so it really depends on the business. For me, I refresh the calendar once a year when I file my federal return and mark all dates until the return the following year.

Also, get an account with EFTPS (https://www.eftps.gov/eftps/), which makes it easier to make payments. They have to snail mail you a pin code, so register sooner rather than later to account for the delay.

Quickbooks Self Employed has been great for taxes. It has built in support for quarterly taxes, and estimates what you owe throughout the year.