looks like it will be 3% but subject to change each quarter
https://www.irs.gov/newsroom/interest-rates-remain-the-same-for-the-fourth-quarter-of-2020
I couldn't find the 1st quarter 2021 press release, but interest rates haven't changed in the marketplace in the last 90 days, so 3% should be safe
note that normally capital gains is 15% of the profit - that may help you decide how much to pay by Jan 15,
