adding the additional income may be affecting some other things on the return so you need to look at what is changing on the 1040 line by line to result in the higher amount due than expected; deductions or credits may phase out giving the impression of higher tax on the income that was added, or triggering underpayment penalty (if you are on desktop looking at the Fed due ticker that includes any penalty). TT tax calcs are very solid so there will be some explanation for the effective 23%. It will be hard to solve here without more details but I would start with the 1040 and see the changes thru to taxable income on line 15 etc.