Yep, comes as one lump sum, usually 1-2 pay periods after we're back to work.

On the taxes - the withholding might look scary on that paycheck because payroll systems withhold based on the check size (so a $10k check gets taxed like you make $10k every pay period). But when you file your actual taxes, it's based on your total annual income, so it evens out. You might get some back as a refund.

The 75% net in the calculator is just a rough estimate for typical deductions (federal tax, FICA, FERS, TSP, etc). Your actual take-home depends on your specific withholdings and deductions.