3 Property Investment Rules for Building Long-Term Wealth

By Mark Parham

If I could go back to when I first started investing in property and give myself three pieces of advice, I’d choose these: understand what you’re buying, give it time, and be careful who you listen to. Those property investment rules matter more to me than finding the perfect house or predicting the next move in the market.

I’ve been investing for around 15 years. I’ve owned property through Brexit, Covid, rising prices and much more expensive mortgages. I’ve made mistakes as well as good decisions. What those experiences have taught me is that building wealth involves more than getting a deal over the line. You need to be able to keep going when the conditions change.

I’m a big believer in getting rich in time with property. That means buying sensibly, understanding the risks and leaving yourself enough room to survive the difficult years. Here’s how I think about it.

You can also watch my original three property investment rules video on YouTube, published on 26 September 2026.

Rule one: understand exactly how the property makes money

Never invest in something you don’t properly understand. It sounds obvious, but people break this rule surprisingly easily when a particular strategy becomes fashionable.

Someone hears that serviced accommodation produces huge returns and decides they want to do that. Then somebody else talks about HMOs, and suddenly an HMO becomes the answer. The strategy gets chosen before the investor has understood the work, the costs or the risks involved.

Before I put money into a property, I want to understand what I’m buying, what it’s worth, what rent it should achieve and what the mortgage will cost. I also want an answer to the question that can get lost in an exciting sales pitch: what happens if something goes wrong?

You don’t need to know everything. I’m still learning after 15 years. But there’s a difference between learning as you go and committing money without understanding where the return is supposed to come from.

Rent isn’t the same thing as profit. Borrowing, repairs, management, insurance, empty periods and tax can all change what you actually keep. Equally, a property’s estimated value isn’t cash sitting in your bank account. Being clear about those distinctions makes the whole decision easier to assess.

For a practical starting point, use the buy-to-let deal calculator. Put your own assumptions into it, then question those assumptions. A neat result is only useful if the purchase price, rent and costs behind it are realistic.

Understand the mortgage risk as well as the opportunity

Leverage is one of the reasons I like property. A mortgage lets you control an asset without paying its entire purchase price from your own cash. But the borrowing that helps you buy the asset also creates a commitment you have to service.

A mortgage at 3% feels very different when it refinances at 6%. I’ve experienced that across my own portfolio. In the video, I explain that my average mortgage rate moved from around 3% to around 6% on about £2 million of borrowing.

That three percentage point increase works out at roughly £60,000 a year in additional interest, or £5,000 a month, using the same borrowing balance. That’s a substantial change in the amount of money the properties have to cover.

My portfolio remained cash flow positive because the properties were bought sensibly and there was enough room in the deals to absorb it. That is my experience, not a promise that somebody else’s portfolio would cope with the same increase.

The wider risk is also recognised in the Bank of England’s analysis of buy-to-let financial stability. Its December 2023 research explains how higher financing costs can put pressure on landlords. I use that as background to the risk, rather than as a description of today’s mortgage offers.

Before buying, I’d want to see the numbers at a more expensive borrowing rate, not just the rate that makes the purchase look attractive. The mortgage stress calculator helps you explore that, and my guide to leverage in property investing explains the principle in more detail.

Rule two: give wealth building enough time

Social media can make patient investing feel as though you’re doing something wrong. Everybody wants to know how to buy ten properties in two years, use none of their own money and become financially free immediately.

I’ve spent around 15 years building my portfolio. Could I have gone faster? Probably. I could have borrowed more and accepted more risk. But speed isn’t the only measure that matters. I’ve become increasingly convinced that investing is partly about staying in the game long enough for the assets to work.

Covid almost destroyed my business. My income changed massively, and life looked very different from how it had looked a year earlier. Later, the financing cost of my property portfolio increased by that £60,000 a year. Both periods taught me how valuable breathing room is.

An investment that only works when absolutely everything goes to plan is a different proposition from one that can cope with setbacks. Buying another property quickly isn’t much of an achievement if it leaves the rest of your finances unable to absorb an ordinary problem.

Imagine buying one decent property each year for ten years. That’s an illustration of a patient approach, not a purchasing target everyone should follow. You’re choosing carefully, collecting rent and allowing time for the portfolio to develop instead of trying to manufacture instant financial freedom.

My long-term view is that rents and property values can grow, while inflation can reduce the real burden of a fixed amount of debt. None of that means prices or rents rise every year. Inflation doesn’t pay money off an interest-only mortgage either: the pounds owed still have to be repaid. Those distinctions matter when turning a broad investment idea into an actual plan.

Leave room in the deal and money in the bank

I’ve watched Dave Ramsey, and his approach helped inspire this video. I don’t share his general preference for clearing almost all debt before investing. Sensible leverage has played a major part in building my property portfolio and my wealth.

But I agree with the need for financial breathing room. If every available pound has gone into deposits and you’ve borrowed everything a lender will offer, a relatively small problem can become a large one.

That’s one reason I care about buying below market value. In the video, I use the example of buying a property worth £150,000 for £135,000. The difference is £15,000 of equity before purchase costs, assuming that £150,000 valuation is sound.

That isn’t £15,000 of immediately spendable profit. Costs still matter, valuations can be wrong, and accessing equity depends on a sale or suitable finance. The point is that the price you pay can give you a margin that simply paying the full value wouldn’t provide.

Combine a sensible purchase price with cash flow and money left in the bank, and you have more options when circumstances change. I want those options. I don’t want every decision forced on me by the next mortgage payment.

Rule three: be careful whose advice you follow

Property has an extraordinary ability to make simple ideas sound complicated. People use acronyms and financial language until you start assuming they must know what they’re talking about.

I judge it differently. Can the person explain the investment in a way that makes sense? If someone presents a deal and, an hour later, you still don’t understand how you’re supposed to make money, I wouldn’t invest in it.

You should be able to explain what you think the property is worth, what you’re paying, what rent you expect and roughly what remains after the main costs. You should also understand which parts are estimates and what would happen if those estimates prove optimistic.

That applies to me too. Don’t invest simply because you’ve watched my videos or because I own a property portfolio. If I talk about refinancing, leverage or buying below market value and something doesn’t make sense, question it.

There’s nothing embarrassing about saying, “I don’t understand this yet.” It’s a useful sentence. It gives you permission to pause, ask for an explanation and work out whether the investment suits your circumstances before money is committed.

Experience can make someone’s explanation useful, but it doesn’t remove your responsibility to understand the decision. I would rather take a little longer to get clear on a deal than discover afterwards that I had misunderstood the risks.

The cash reserve underneath all three rules

Keep some cash available. I’ve learnt the importance of that the hard way, and I’ve become more cautious about it as my portfolio has grown.

In the video I talk about three to six months of expenses as an emergency-fund starting point. The right amount is personal. It depends on your commitments, the properties you own and the problems you might need to absorb. It isn’t a guarantee that any particular reserve will cover every situation.

Cash gives you time. If a tenant leaves or a large repair bill arrives, you can deal with it without immediately selling something or reaching for expensive borrowing. A valuable property doesn’t necessarily solve a bill that needs paying this week.

My article on cash reserves for property investors goes further into that distinction. The aim is to build a portfolio you can hold through difficult periods, not just one that looks impressive when you add up its estimated value.

Put the rules to work before your next purchase

Before committing to a property, I’d bring the decision back to three questions. Can I explain how it makes money and where the risks sit? Can I afford to give it time without depending on everything going right? Am I relying on evidence I understand rather than somebody else’s confidence?

Then I’d check the cash remaining after completion. Those questions won’t remove investment risk, but they can expose assumptions that deserve attention before they become expensive mistakes.

If you’d like to talk through your next step, you can book a free 30-minute strategy call. For ongoing learning, explore Starter Club, or find out about Done For You if you’d like to understand that service.

My approach is fairly simple: understand the investment, be patient, question what you’re told and leave yourself room to cope. Do those things consistently and you give yourself a much stronger foundation for building wealth with property over time.