118 guides on finance. Showing the 48 most recent.
Interest, tax, salary and what a number does over time. These guides work from the rules and the reference rates that set each figure, and say which year an amount applies to — a threshold restated every January is worth nothing without the year attached.
Ranked by how many pages of this site link to them, not by traffic.
On $52,000 a year, a fortnightly cheque is $2,000 and a twice-monthly one is $2,166.67. The second looks 8.33 % better and pays exactly the same — because there are 26 of the first and 24 of the second.
Camille Laurent · 3 min read
Eight points of excess return over a beta of 1.2 gives 6.67. Change the beta to 0.6 and the same portfolio scores 13.33 — the number moves entirely on an estimate.
Camille Laurent · 3 min read
A price of 120 including 20 % tax has a net of 100, not 96. Subtracting 20 % of the gross is the most common invoicing error there is, and it always errs the same way.
Camille Laurent · 3 min read
10,000 growing at 7 % a year becomes 19,671.51 after ten years — a rise of 96.7 %. The rule of 72 predicted 10.3 years to double, and it was right to within four months.
Camille Laurent · 3 min read
Buy and sell fees of 0.5 % each need a 1.005 % gain to break even. Triple them to 1.5 % and you need 3.046 % — more than triple, because the two fees multiply rather than add.
Camille Laurent · 3 min read
CAPM and the dividend growth model both compute the cost of equity. On one set of inputs they give 9 % and 7 % — and the choice between them decides a valuation more than any figure inside either.
Camille Laurent · 3 min read
A payment of 1,000 a year is worth 20,000 at a 5 % discount rate and 25,000 at 4 %. The formula is a single division, and that is exactly why the input matters more than the arithmetic.
Camille Laurent · 3 min read
Ten shares at 100 plus twenty at 80 gives an average of 86.67. Buy forty at 50 instead and it falls to 60 — but the money at risk goes from 2,600 to 3,000.
Camille Laurent · 3 min read
The addition is the easy half. Turning balances into the fewest possible transfers is a different, and much harder, computation — and the tool's own note claims a minimum it does not deliver. Plus uneven shares, and why the awkwardness is ambiguity rather than money.
Camille Laurent · 11 min read
The number is large because it is a daily number multiplied by 260 or 365 — and the same arithmetic works on anything daily, which is the part worth keeping. With the home-brewing comparison done properly, and a plain statement of what the number is not.
Camille Laurent · 10 min read
The addition is trivial. What people miss is the annual plan billed once, the trial that converted, the conversion fee on a service billed abroad — and the break-even month that decides whether a yearly plan was ever a saving.
Camille Laurent · 11 min read
The hourly rate is the small part. Minimum hours, the late-return surcharge, the ride home — and the question that changes the number most: casual help, or a declared employee? Six markets, named, with the thresholds that could be verified.
Camille Laurent · 12 min read
Score both wrappers on the same rows and the pension plan wins the arithmetic at almost every horizon and almost every combination of tax rates — including when the rate does not fall at all. Which is exactly why the deduction is the wrong thing to decide on.
Camille Laurent · 17 min read
The product paying the second-highest headline rate finishes last, and the reason is a tax change that took effect in January 2026. The three French savings vehicles scored on identical criteria: rate, tax, net return, real return, and what each one costs you in access.
Camille Laurent · 17 min read
The usual advice is that a buy-back gets worse with age, because the price rises. The French scale is written to be actuarially neutral, so that is not quite what is happening — and once you see what actually moves the answer, the decision changes. Computed on the current parameters.
Camille Laurent · 14 min read
A missing quarter in France costs you twice over, through two separate mechanisms that most explanations mention only one of. A German point is a single arithmetic step and much easier to price. Both are computable, and the 2026 figures changed more than usual.
Camille Laurent · 14 min read
The 183-day rule is the most repeated and least understood sentence in cross-border work. It comes from one article of one model treaty, it has three conditions and not one, and it decides nothing at all about social security, payroll or your employer's exposure. Here is what each rule actually tests.
Camille Laurent · 16 min read
France lets a parent pass 100,000 euros to a child free of duty and resets the counter every fifteen years. Germany allows 400,000 euros and resets it every ten. On the same 500,000-euro transfer the French bill is seven times the German one, and the gap widens with every decade you have.
Camille Laurent · 10 min read
One flat worth 400,000 euros, one only child, three countries. France charges tens of thousands. Italy charges nothing. Spain charges anything from nothing to 76,000 euros depending on which of its seventeen regions the parent lived in — and that is not an exaggeration.
Camille Laurent · 11 min read
Four European countries, four different answers to the same question: at what point does a small business stop being treated as small? The thresholds matter less than the clock attached to them — some bite the day you cross, others wait for January.
Camille Laurent · 13 min read
The benefit is 90 percent of the first slice of your indexed career average, 32 percent of the next and 15 percent of the rest — 1,286 and 7,749 dollars are the 2026 bend points. Then age adjusts it: claiming at 62 with a full retirement age of 67 cuts it 30 percent, waiting to 70 adds 24.
Camille Laurent · 15 min read
The USDA's figure of 233,610 dollars for a middle-income child born in 2015 — 317,315 restated in 2025 money — is not a sum of receipts. It is allocated household spending, and the housing line is measured as the cost of one more bedroom.
Camille Laurent · 12 min read
PV = FV ÷ (1+r)^n. At 7 percent over 30 years the discount factor is 0.131, so a promise of $100,000 in thirty years is worth $13,137 today — and $41,199 if you assume 3 percent instead.
Camille Laurent · 7 min read
IRR picks the $10,000 project returning 50 percent; NPV picks the $100,000 project returning 30 percent, worth $20,370 against $3,889. And a mine with a cleanup cost has two IRRs, 10 and 20 percent, so the rate answers nothing.
Camille Laurent · 7 min read
EMI = P·i·(1+i)^n ÷ ((1+i)^n − 1). On $300,000 at 6 percent, doubling the term from 15 to 30 years cuts the payment by 29 percent but multiplies the interest by 2.2 — from $155,683 to $347,515.
Camille Laurent · 7 min read
The stop goes where your idea is wrong, not where your comfort runs out — and then the position size adapts to it. Here is the volatility argument, the sizing arithmetic, and the win rate each reward multiple demands.
Camille Laurent · 9 min read
Funding is paid every eight hours on the full notional, between traders rather than to the exchange. A rate of 0.01 percent looks like nothing and costs 10.95 percent a year. Here is the formula and an annualised table.
Camille Laurent · 7 min read
Price impact is arithmetic: on a constant-product pool it equals your trade size divided by the reserve plus your trade. Here is the formula, a table of trade size against impact, and why the setting called slippage tolerance changes none of it.
Camille Laurent · 7 min read
On one twelve-month series the Sortino ratio is 7.7518 or 3.8759 depending only on whether the squared shortfalls are divided by all twelve months or by the three below target. The two conventions differ by exactly the square root of twelve over three, and they can rank two funds in opposite orders.
Camille Laurent · 13 min read
The subtraction is not an approximation of the Fisher relation — it is the exact answer multiplied by (1 + i). At 8 percent nominal and 3 percent inflation the real return is 4.8544 percent, the shortcut says 5, and the error is exactly 3 percent of the answer. Always.
Camille Laurent · 12 min read
The number on the farm's front page is a gross figure before every subtraction. Here is a 120 percent APY walked down, one layer at a time, to the 33.6 percent that actually landed — plus why APR and APY are not the same number.
Camille Laurent · 7 min read
An advertised $32,000 car leaves the lot at $36,399 before any trade-in — $2,324 of sales tax, $500 of doc fee, $375 of title and registration and $1,200 of add-ons. Strip the add-ons and the irreducible gap is $3,115, or 9.73 percent of the sticker.
Camille Laurent · 13 min read
A twelve-year-old roof that costs $20,000 to replace is worth $10,400 on a straight-line schedule. After a $2,000 deductible, an actual cash value policy pays $8,400 and a replacement cost policy pays $18,000 — same roof, same loss, $9,600 apart.
Camille Laurent · 12 min read
Qualified expenses, the K-12 cap and state tax treatment are three separate rules, and only the first two are federal. The K-12 cap doubled to 20,000 dollars for tax years from 2026; a federally qualified withdrawal can still be a state recapture event.
Camille Laurent · 15 min read
At 7 percent nominal and 3 percent inflation the real return is 3.883 percent, not 4. The Fisher equation divides, it does not subtract — and over 30 years the shortcut overstates a $10,000 pot by $1,072.
Camille Laurent · 6 min read
A 6 percent loan with a 3 percent fee and compulsory insurance carries an APR of 10.7 percent and costs $486 more than a 7.5 percent loan with no fees at all. The APR is the figure that catches it.
Camille Laurent · 6 min read
Standard, extended, overpaid, refinanced or income-linked: the same $30,000 at 5 percent costs anywhere from $35,716 to $52,613. And where a scheme writes the balance off, overpaying can cost $11,178 and buy nothing.
Camille Laurent · 6 min read
Settling a $20,000 car loan at 7 percent two years in saves $1,431 of interest — but only $663 of that is a real gain if the cash was earning 4 percent, and precomputed interest can take $62 or more off the top.
Camille Laurent · 6 min read
A 1:3 ratio does not make you right more often — it lets you be wrong three times out of four and still break even. Here is the inversion, a table of ratio against required win rate, and what costs do to both.
Camille Laurent · 6 min read
Market cap is price times circulating supply — an arithmetic product, not money invested. Volume is what actually changed hands. Here is what each measures, how their ratio exposes a thin market, and where fully diluted valuation fits.
Camille Laurent · 7 min read
An advertised 8 percent becomes 8.33 percent once daily rewards compound — and then 7.46 percent after a 10 percent validator commission, and less again after unbonding time. Here is each step, with the arithmetic laid out.
Camille Laurent · 6 min read
Impermanent loss is not a fee and it is not temporary: it is the gap between your liquidity position and simply having held the two tokens. Here is the formula, a table of price change against loss, and the fee income you would need to come out ahead.
Camille Laurent · 6 min read
Split $50,000 into five rungs instead of one five-year deposit and you end year five with $61,573.20 instead of $61,715.12. The whole liquidity option costs $141.92, once, during the ramp — and it is worth $1,049.24 if rates rise a point.
Camille Laurent · 12 min read
Sell at $700,000 with a $300,000 basis and the gain is $400,000. Buy back at $640,000 and the $60,000 you kept is boot — taxed now, at 25 percent, because it is depreciation coming home. The 45 and 180 days start on the same day; they do not run one after the other.
Camille Laurent · 15 min read
Standard rates run from 17 percent in Luxembourg to 23 percent in Ireland and Portugal, with Switzerland outside the EU at 8.1 percent. The full table, with reduced and zero rates and an honest as-of date.
Camille Laurent · 7 min read
Zakat is 2.5 percent of qualifying wealth held for a lunar year — but the threshold at which it becomes due has two classical definitions, one in gold and one in silver, and today they differ by roughly a factor of twelve. Here is why, and what each side argues.
Camille Laurent · 16 min read
Spending $40,000 a year needs $1,000,000 at 4 percent and $1,333,333 at 3 percent. Where the number came from, what it measured, and the four objections that matter.
Camille Laurent · 6 min read
A $50,000 machine with a $5,000 salvage value and a five-year life. Straight line deducts $9,000 in year one, double declining balance $20,000, and MACRS $10,000. The lifetime total is the same; only the timing moves — and the timing is worth about $320.
Camille Laurent · 15 min read