Series
quant finance
15 parts, in reading order. Each one builds on the last.
- 01
Quantitative finance in ten ideas
AUG 30 2026 · 7 min
Ten ideas carry most of quantitative finance: returns multiply, risk scales with the square root of time, correlation decides how much risk cancels, an…
- 02
What is quantitative finance?
AUG 31 2026 · 13 min
Quantitative finance is the practice of making investment and risk decisions from measured numbers and tested rules rather than judgement alone.
- 03
Probability: how often something happens
SEP 5 2026 · 10 min
A probability is a number between 0 and 1 that says how often something happens in the long run.
- 04
Expected value: what a risky choice is worth on average
SEP 11 2026 · 9 min
Expected value is the average result you would get if you could repeat a risky situation many times: multiply each possible outcome by its probability and add…
- 05
Returns compound: multiply, never add
SEP 17 2026 · 10 min
Returns chain by multiplying growth factors, not by adding percentages, and that one fact explains why +50% then −50% loses money, why a five-year gain is not…
- 06
Mean and standard deviation: return and risk in two numbers
SEP 19 2026 · 9 min
The mean tells you where the middle of your data is, and the standard deviation tells you how far a typical value strays from that middle; in finance the first…
- 07
Value is an estimate: discounting, growth and the margin of safety
SEP 21 2026 · 8 min
A price is observed; a value is estimated.
- 08
Why prices are hard to beat: efficiency, random walks and a roulette wheel
SEP 24 2026 · 10 min
An efficient market is one where no reliable edge survives after costs, because any pattern worth money is traded away by the people who find it.
- 09
Covariance and correlation: why a mix is safer than its parts
SEP 27 2026 · 10 min
Covariance and correlation measure whether two things tend to move together; in a portfolio, that one number decides how much of the risk cancels out, which is…
- 10
Data that lies: the bugs that look like alpha
SEP 29 2026 · 8 min
Most of the alpha in a backtest is a data bug with a name: a feature that used tomorrow's number, a universe built from today's survivors, a thousand ideas…
- 11
What a trade really costs
OCT 2 2026 · 9 min
A trading idea becomes profit only after paying the bid-ask spread, walking the order book, moving the price and, for a short, borrowing the shares.
- 12
Sharpe, Sortino and information ratio: return per unit of risk
OCT 4 2026 · 12 min
A return on its own means little until you know the risk taken to get it; these three ratios divide extra return by risk, and they differ only in what they…
- 13
Beta and alpha: how much of the market you carry, and what is left
OCT 6 2026 · 9 min
Plot a stock's daily return against the market's and fit a straight line.
- 14
Portfolio optimisation: choosing the weights
OCT 9 2026 · 10 min
Portfolio optimisation chooses how much to put in each asset so that, for the risk you accept, the expected return is as high as possible; it works because…
- 15
Backtesting in Python
OCT 15 2026 · 16 min
A backtest runs a trading rule over past prices and reports what would have happened: the return, the risk, the number of trades.