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Camille Laurent

Articles by Camille Laurent

Finance writer · View profile

· 12 min read

Hashtags Are a Search Index, Not a Megaphone

A hashtag makes a post findable in a query, which is a different job from making it spread. Model the visibility a tag actually buys and the answer falls out: a tag's worth is its viewers-per-post-published, not its volume — so a very popular tag returns almost nothing and a specific one returns twenty-five times more.

· 12 min read

When to Post, and Why the Answer Is Mostly Not the Time

Published best-time tables average over audiences that are not yours, and on a ranked feed posting time matters far less than it did on a chronological one. Compute your own audience's activity across time zones instead — six zones flatten the timing lever from a 94% swing to a 22% one — and see how many posts a real timing test needs.

· 12 min read

Social Image Sizes, and the One Crop That Survives Everywhere

Platforms crop rather than letterbox, so an image is only safe if its subject sits inside the intersection of every ratio it will be shown at. That intersection has a closed form — the narrowest ratio divided by the widest — and it works out at 29.45% of the source for a realistic set. Geometry that does not expire, plus the pixel counts that do.

· 12 min read

What an Email Programme Actually Returns

The famous email ROI multiples are self-reported survey figures with the labour left out of the denominator and revenue that would have arrived anyway left in the numerator. Build the honest version instead: incremental revenue against full cost, measured with a holdout — and the arithmetic of how big that holdout has to be.

· 12 min read

Open Rate Is a Measurement of Your Audience's Mail Client

The denominator should be delivered, not sent — which means defining hard and soft bounces properly. Unique and total opens are different numbers. And a reported open rate has a computable null point: past a certain share of prefetching clients it carries no information about humans at all. The instrumentation that replaces it.

· 13 min read

Cost Per Click, and What You Are Actually Bidding Against

Your bid decides whether you are eligible; the advertiser below you decides what you pay. Doubling a bid can move the price not at all, quality can halve it for the same position, and the average CPC in your report is a click-weighted mixture that describes no query. The auction arithmetic, worked.

· 13 min read

What Makes a URL Slug Good: Stability, Readability and the Conflict Between Them

A slug has two jobs that pull against each other: it is a permanent identifier and it is a piece of readable text. Length, hyphens, stop words, dates, non-ASCII characters and the identifier-plus-slug pattern that gets both properties — with the real numbers from a site that localises 1,736 tool slugs into six languages.

· 2 min read

APR vs APY: What's the Difference?

APR and APY both describe a yearly rate, but only APY includes compounding. Here's what each means and which one actually matters for savings and loans.

· 3 min read

How Much House Can I Afford?

The income-multiple and 28/36 rules give you a ceiling in minutes. Here's how to work out an affordable price from your income, debts and down payment.

· 2 min read

How Does Compound Interest Work?

Compound interest is interest earning interest. Here's the formula, a worked example, and why starting early beats saving more later.

· 3 min read

How to Calculate VAT (Add and Remove It)

VAT is a percentage added to a price. Here's how to add VAT to a net price, remove it from a gross price, and find the tax amount — with examples.

· 2 min read

How Are Mortgage Payments Calculated?

Your monthly mortgage payment comes from three things: the amount borrowed, the interest rate and the term. Here's the formula and what moves the number.

· 2 min read

Gross vs Net Pay

Gross is what you earn; net is what you keep. Here's what comes out in between, and why you should always compare job offers on net pay.

· 2 min read

Markup vs Margin: What's the Difference?

Markup and margin both describe profit on a sale, but from different bases. Confusing them costs money — here's how each works and how to convert.