See this TurboTax support FAQ for calculating the estimated taxes - https://ttlc.intuit.com/community/tax-payments/help/can-turbotax-calculate-next-year-s-federal-estim...
Or use the worksheets for the IRS Form 1040-ES to calculate your estimated taxes - https://www.irs.gov/pub/irs-pdf/f1040es.pdf
Estimated taxes can be paid directly to the IRS using the IRS payment website - https://www.irs.gov/payments
