Three types of tax, and making sure you are paying only the right ones
For freelancers, or Freiberuflich, you will have registered your business through the tax office and will be sent your tax number via the mail. For Gewerbetreibende, more likely a trade profession, you register with Gewerbeamt, who will relay your application to the Finanzamt who will issue your tax number via mail.
There are three key taxes: Income Tax, VAT and Trade Tax. In addition to this, you may be required to pay social security provisions, and every person is required by law to have health insurance - for freelancers this means paying for it themselves on an annual or monthly basis. While it is not a tax, should be factored into the fixed cost as such. For the purposes of this article, we are going to assume you are just a freelancer and also that you are within your first two years of business. Which brings us to our next point, and back to VAT for a second:
According to §18 of the Umsatzsteuergesetz (VAT law) for the first 2 years after starting activity, you will have to do a VAT announcement (Umsatzsteuervoranmeldung) each month AND pay each month as well. For example, if you had a net turnover of 2000 EUR plus 190 EUR VAT in April 2016, you have to electronically announce that to the Finanzamt electronically by May 10th, 2016 AND have also transferred the 190 Euro into the Finanzamt's bank account by May 10th, 2016. You already know about the obligatory electronic announcement, but I'll bring it here nevertheless for people who (wrongly) think it's a big deal because it's not.
The Umsatzsteuervoranmeldung can be quite straightforward once you know your way around it, the Finanzamt has a software you can download, ELSTER and learn more how to use it: Freelancers Guide To ELSTER, where you fill in your name, address, tax number and the money you TOOK IN (turnover) for the last month and software calculates the VAT, you also fill in the summed amount of any invoices you PAID, and it then calculates the difference between the two VATs, which is the amount you will have to transfer to the Finanzamt that month.
You then send that filled in form to the Finanzamt just by clicking send (ok, choose in the menu " Datenübermittlung ‘’data transfer", the entry " Steuererklärung an das Finanzamt übermitteln = send to Finanzamt") and you don't even need a certificate to do it, so anybody who knows your tax number can do it (and since you have to print your tax number on all your invoices the door is wide open to nasty practical jokes...). No, not really, that's fraud! But chances are that you are well versed in Tax-ology and tax life at the point of two years in, so it is about assessing what is right for you and congratulations on making it the first two years!
The German Tax Year, a general look
The German tax and financial year follows a standard calendar year - meaning your financial year begins on January 1 and ends on December 31. Income Tax is most likely paid quarterly, in advance, based on pre-payment estimates from the Finanzamt. It can, at times, take two years to have accurate prepayment figures. VAT is most likely reported monthly, however, this can also be done on a quarterly term - either way, it too often carries pre-payment basis.
Trade Tax is also paid quarterly in the same circumstances as the income tax. Then, annually, you will complete a tax assessment once the financial year closes - which reports on your entire income, taxes, deductions, expenses and revenues. The deadline for this is the 31st of July in the following financial year. Therefore, your 2019 tax assessment must be completed and submitted to the Finanzamt by July 31, 2020. Having a Steuerberater can help communicate with the Finanzamt should you be having issues, but generally, keeping to the deadlines ensures no nasty issues with the Finanzamt.