Investment & Investing

How do you compare a salary sacrifice pension vs investments? If you are in the higher tax bracket you get a lot of "free" money but that doesn't compound over time like interest.

Not entirely true. That money is used to buy allocations, those allocations provide a dividend, that dividend is re-invested. And it continues.

Is there a point where a fund would outperform the pension over 20 to 30 years?

Yes, for lots of reasons. But I think you have things a little muddled; a Pension is usually invested in a 'fund'. I think what you really mean is would chucking stuff in the equivalent ISA be better long term, and the simple answer is yes if you have a lot of money, and no if you do not.