How and when do I pay estimated taxes at the federal and state levels?

Federal Estimated Tax is paid with form 1040-ES.  You would compute the amount of tax you think you owe, less any withholding on W-2 jobs that you expect. There is a booklet and worksheet to help you figure out whether to pay based on this year's expected tax hit or last year's actual tax liability.  Then you would take the amount you owe and pay 1/4 of it each quarter. Note that the government defines its "quarters" differently from what you might expect.1st quarter is due on April 15 (often 1-3 days later due to a holiday in Washington DC--this year it's due April 18)2nd quarter is due on June 15 (!)3rd quarter is due on September 154th quarter is due on January 15 of next year (sometimes 1-3 days later depending on MLK day)California has a similar form, the 540-ES. However, California has an unpleasant twist in its estimated tax. This was enacted several years ago during some budget crises, but it is encoded in the law and has not been reset. The quarterly due dates are generally the same as Federal law, but the amount is not 1/4 each time. Instead, you pay:30% of the amount you owe on April 1540% of the amount you owe on June 150% (zero!) on September 1530% of the amount you owe on January 15 of next year.Because governments use cash accounting and the California fiscal year ends June 30, having you pay 70% of your total estimated tax brings income forward for the state. Of course, doing this requires taxpayers to dip into their own cash reserves to pay 70% of their expected tax when they may well have earned less than 50% of their potential income.There is a complicated method of figuring your estimated tax that tracks when the actual income was earned and the actual tax was paid. If your income is highly uneven, this may be advantageous, especially if you earn a lot in the second half of the year. Otherwise, paying the required installments based on one of the methods using current year or last year is simpler.

https://www.mileiq.com/blog/tax-planning-for-self-employed/I think the answers here and this easy-to-read guide should help.