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Camille Laurent

Articles by Camille Laurent

Finance writer · View profile

· 2 min read

The 50/30/20 Budget Rule

Split after-tax income into 50% needs, 30% wants, 20% savings. Here's how the buckets work, what counts as each, and how to adapt it to your life.

· 3 min read

How to Calculate Your Break-Even Point

Your break-even point is where revenue equals costs. Here's how to find it in units and revenue, and how to use it to make pricing decisions.

· 2 min read

What Is a Good Credit Utilization Ratio?

Credit utilization is the share of your credit limit you're using. Here's what counts as good, why it matters for your score, and how to lower it.

· 3 min read

How Much Should You Save for Retirement?

Save around 15% a year and aim for roughly 25 times your annual spending. Here's the rules of thumb, why starting early matters, and how to find your monthly number.

· 2 min read

How Big Should Your Emergency Fund Be?

Three to six months of essential expenses is the usual rule. Here's how many months fit your situation, where to keep the money, and how to build it.

· 13 min read

Title Tags, Meta Descriptions, and What Search Engines Do With Them

What Google's own documentation says about rewriting title links and about the meta description, rather than what SEO folklore says. Then the measurable part: titles are truncated by pixel width, so two titles of exactly sixty characters can render 204.55 pixels apart and only one of them survives.

· 2 min read

What Is the Debt-to-Income Ratio?

Your debt-to-income ratio compares your monthly debt payments to your income. Here's how to calculate it, why lenders use it, and how to improve it.

· 11 min read

Growing an Email List Is a Leaky Bucket

Constant additions against a proportional loss rate do not grow forever — they converge on a ceiling equal to additions divided by the loss rate. Here is that ceiling computed for six loss rates, why a list can grow while its engaged half shrinks, and the feedback loop that makes a bought list self-defeating.

· 11 min read

The Lead-to-Customer Rate, and Why It Is Not One Number

The overall rate is the product of the stage rates, which makes a percentage gain anywhere worth the same percentage overall — and a ten-point gain worth wildly different amounts depending on where you put it. Plus the lag that makes a growing business look worse than it is.

· 11 min read

What an Investment Return Number Is Not Telling You

A fund can return 9.49 percent a year while its investor earns −1.77 percent. Time-weighted versus money-weighted, nominal versus real, gross versus net — four questions inside one number, separated with arithmetic.

· 10 min read

Consolidating Debt Moves It, and Sometimes Costs More

Four balances of $20,000 at 20.6 percent blended, cleared on a $680 budget, cost $7,085 in interest. One loan at 9.9 percent over seven years cuts the payment to $330.99 — and costs $7,803. The break-even term is 77 months.

· 2 min read

How to Calculate a Tip and Split the Bill

Multiply the bill by the tip percentage, add it on, then divide by the number of people. Here's the method, an example, and how tipping norms differ.

· 12 min read

The 4 Percent Rule Is a Result From One Country and One Century

The rule is the output of a named backtest on US data. Its inversion, 1 ÷ w, gives the multiple: 25× at 4 percent, 33.3× at 3 percent. And two paths with the same 4.7676 percent geometric mean end one at zero and one at $2,031,661.

· 16 min read

Leverage, Liquidation, and the Asymmetry of Losses

Liquidation distance is (1 ÷ L − m) ÷ (1 − m): at 20× that is 2.56 percent on a 2.5 percent maintenance margin, inside a normal day. Recovering a loss needs 1 ÷ (1 − L) − 1, so 90 percent lost needs 900 percent back. Combined, repeated leveraged bets on a market with a genuine +0.08 percent edge compound at −1.23 percent per period at 10×.

· 14 min read

Dollar-Cost Averaging: What It Actually Buys You

Spending a fixed amount each period buys more units when the price is low, so your average cost is the harmonic mean of the prices while the average price is the arithmetic mean — always lower, by 4.10 percent on the path worked through here. Against a lump sum, a 200,000-path simulation puts DCA's standard deviation 41 percent lower and its expected terminal wealth $337 lower on $12,000.

· 15 min read

Volatility Is Not Risk, and the Square Root of Time Is a Choice

Annualised volatility = period standard deviation × √(periods per year), and that √t scaling assumes independent increments. It is a model, not arithmetic: at a daily autocorrelation of 0.1 a 60 percent annualised figure should read 66.3. The payload is volatility drag — the arithmetic mean exceeds the geometric by about σ²/2, so at 8 percent average return and 40 percent volatility the compound outcome is zero.

· 2 min read

The Rule of 72, Explained

The rule of 72 estimates how long money takes to double: divide 72 by the interest rate. Here's why it works, when it's accurate, and how to flip it.

· 15 min read

The Sharpe Ratio, and What It Quietly Assumes

Sharpe = (return − risk-free) ÷ standard deviation, so it prices return per unit of volatility — and volatility is symmetric. Two funds can share a Sharpe of 0.4939 while their Sortino ratios are 8.59 and 0.74. Annualising by √12 assumes independent returns: at an autocorrelation of 0.2 the published figure is 20 percent too high.

· 3 min read

How to Calculate Your Net Worth

Net worth is what you own minus what you owe. Here's how to total your assets and debts, what to include, and why the trend matters more than the number.

· 3 min read

How Inflation Eats Your Savings

Inflation quietly cuts what your money can buy. Here's what it is, how it erodes cash, the rule of 72 for prices, and how to protect your savings.