If you are self-employed, you are generally required to make estimated tax payments to the IRS to cover your expected income tax plus self-employment tax. These estimated payments are due 4 times a year (generally April 15, June 15, Sept 15 and January 15). Your tax return calculates your actual taxes owed. If you made more estimated payments than you owe, you get a refund, and if you owe more than you paid, you must pay the difference when you file your return. If you don't make estimated payments during the year, you can be charged an under-payment penalty even if you pay in full when you file your return.
It is too late to make estimated payments for the 2020 tax season, just file your return and pay what you owe. Your first estimated payment for the 2021 season is due May 17 (the deadline was extended).
However, the exact amount of that payment that is credited to you social security account depends entirely on your taxable income earned from working, and you can't decide to pay more to build up a retirement fund.
