The arithmetic behind every investment decision.

Net rental yield is annual rent minus every running cost, divided by the purchase price plus every acquisition cost, and it is typically two to three percentage points lower than the gross yield a listing advertises.

The only fair rent versus buy comparison is unrecoverable cost against unrecoverable cost: the rent you pay against the interest, service charges, opportunity cost and amortised transaction costs of owning, which together usually come to about five percent of the property value each year.

Two off-plan payment plans quoted at the same headline price are not the same price, because money paid later costs less in present value, and the gap between a front loaded plan and a post handover plan is commonly five to fifteen percent of the headline figure.

Cash on cash return is the annual cash left after every running cost and every mortgage payment, divided by the cash you actually put in, and it is the only property return figure that answers what your own money earned.

The round trip cost of buying and selling property is roughly eight to ten percent of value in Dubai, and because that cost is fixed regardless of how long you hold, it sets a minimum hold period below which a purchase cannot pay for itself.

The three fund portfolio holds a total domestic equity fund, a total international equity fund and a total domestic bond fund at market weights, and its weakest assumption is the word domestic, which has no meaning for an investor with no home bond market.

All Weather is Ray Dalio's framework holding that every economic environment is a combination of growth and inflation either rising or falling, and that a portfolio should hold assets that win in each of the four resulting boxes rather than betting on which one arrives.

Vanguard's research across US, UK and Australian markets found that investing a lump sum immediately beat spreading it in over twelve months in roughly two thirds of the historical periods tested, because markets rise more often than they fall.

The safe withdrawal rate is the share of a portfolio you can spend in the first year of retirement, increasing with inflation thereafter, without running out of money, and current credible estimates range from about 3.9 percent to about 4.7 percent depending on the assumptions.