Buying £100 for £80? That doesn’t sound like a very likely offer. However, this seems to be exactly what a self-funded personal pension (SIPP) offers. In fact, depending on the level of income tax you pay, that £100 could cost even less than £80.

What happens if it sounds potentially too good to be true?

Tax breaks are like free money

The clue is that higher or additional rate taxpayers could potentially receive even more so-called free money.

Essentially, a SIPP offers tax relief, reflecting the tax you’ve already paid on the money you then put into it.

So it’s not exactly “free moneyThe State Treasury basically takes your hard-earned money with one hand and gives some of it back with the other.

But why look a gift horse in the mouth?

It may be a tax break rather than a magic money tree, but the SIPP structure still means that even a basic rate taxpayer can have £100 to invest for every £80 they contribute to their SIPP. It definitely seems worth considering.

A SIPP is very different from an ISA

While the SIPP structure offers advantages, it is crucial to understand that it also comes with limitations.

This is not just another version of an ISA like the Lifetime ISA. It’s a completely different product designed to support people plan their finances for retirement.

This objective is reflected in the fact that an investor cannot withdraw a penny from their SIPP before the age of 55.

This can support provide discipline when building your pension pot, but means there is much less flexibility in withdrawals compared to an ISA or share trading account.

Even at the age of 55, they can’t just take whatever they want from their SIPP tax-free. There is a tax-free allowance: up to a quarter of the SIPP value. The remainder would be taxable when withdrawn, although, like an ISA, it can be deposited tax-free before withdrawal.

Still, despite its limitations, a SIPP may be worth considering as an investment vehicle. For many investors, tax relief can be an crucial financial motivator.

Thinking about the stock market in decades, not days

I also see the benefit of SIPP in forcing me to take a long-term approach to retirement planning. As a long-term investor, this is consistent with what I’m trying to do anyway.

An example from my own SIPP in which I have shares Rockwood’s strategy (LSE: RKW). The investment fund focuses on miniature UK companies, many of which may not even be on my radar as an investor.

It focuses on creating long-term value. This helps explain why it doesn’t typically pay a dividend. However, long-term share prices are solid, with Rockwood’s share price up 79% over the last five years.

Small businesses can struggle in an economic downturn, and that’s the risk I see for Rockwood’s strategy in current market conditions. It does well owning miniature companies like supplier SpaceX Filtronicbut farms like STV have been struggling with this problem lately.

Over time, I expect Rockwood’s ability to evaluate miniature companies with growth and earnings potential could support it perform well. I’m content to keep it in my SIPP and have no plans to sell it.