In my taxable investment account will taking 20k in long term losses offset 10k in long term gains, and any of 10k in interest and 12k in dividends?

@Timbo99 the long term losses will certainly offset the long term gains.   otherwise, the losses can only offset up to $3000 of ordinary income (the interest and the dividends) each year.  In your example, the remaining $7000 of losses are carried over to 2024.