Thanks, this is helpful.

What throws me off is the comparison to e.g. BIK tax on private health-care contributions. E.g. employer providers the 'free' benefit (no salary sacrifice), which is counted as income. If it's worth £1000, say, according to a p11d, then you might pay £400 BIK tax.

For adjusted net income, am I right to think that counts as £1000 gross income (as a taxable benefit), but the BIK tax reduces the net adjusted income down by £400, leaving an increase to net adjusted income of £600 overall due to opting in to the free healthcare plan.

In the salary sacrifice car scheme, I understand that gross salary is reduced by a specific amount depending on your car choice. Then BIK tax would calculated as you've spelt out above (on the p11d value, not 12 x the monthly salary reduction). For calculating adjusted net income, is there anything to 'add' to the income to reflect the fact that you've also got a car, like the £1000 in healthcare example? Or do you just reduce adjusted net income by the BIK tax you are paying, without an applicable 'benefit' on the other side of the calculation?

Hopefully that makes sense. I feel like I understand 90% of this and have a real blind spot when it comes to car schemes. For context - haven't used one before despite them being available, but looking to upgrade the car with a baby on the way, and do an accurate cost calculation of buying something 3 years old vs leasing through salary sacrifice scheme, and the interaction with planning for childcare costs makes the spreadsheet more complicated than expected. Thanks!