Financial calculator guides
Financial calculator guides, formulas and examples
Plain-language guides to interest, options payoffs, mortgages, retirement modelling and tax estimates. Every guide states what the model includes, what it leaves out and which calculator lets you test the assumptions.
Options
Stock options vs index options: which strategies fit which
Single-name gap risk versus index diversification, applied to strategy choice.Options
SPX vs SPY options explained
Cash settlement, exercise style, trading hours and 0DTE, compared.Options
Best stocks and ETFs for covered calls: the traits that matter
Liquidity, IV level and catalyst risk — not a list of tickers.Options
Covered calls for income, explained
What caps the income, and how cash-secured puts extend the idea.Options
LEAPS options strategies explained
Why a longer-dated option costs more but decays slower per day.
Retirement
How to model retirement savings with monthly contributions
A step-by-step walkthrough of balance, contribution, rate and time.
Investing
CAGR explained: formula, uses and what it hides
Why one annualized rate can mask volatility and cash flows.Mortgages
When to refinance: the break-even point explained
How closing costs, savings and loan term interact.
Savings
How much to save each month to reach a goal
The backward calculation behind a savings target.Loans
APR vs interest rate: what the difference means
Why APR is usually higher, and where it can still mislead.
Housing
Is it better to rent or buy?
How time horizon flips the cost comparison.
Inflation
Inflation and purchasing power explained
Checking whether your savings rate keeps up.Mortgages
How mortgage amortization works
Why early payments are interest-heavy, and what changes that.Investing
Gold and commodity investing, modeled honestly
Why price is the only lever, and what an assumed rate leaves out.Mortgages
Home equity and HELOCs, explained plainly
How loan-to-value limits turn equity into a borrowing ceiling.Compensation
A stock grant isn't yours until it vests
How a cliff and vesting period turn a grant into ownership.Options
Margin buying power is a limit, not a target
How initial and maintenance margin set what you can borrow and keep.Investing
Cost basis and averaging down explained
How blended average cost is calculated, and why lowering it isn't the same as lowering risk.Investing
How to calculate stock profit and loss
Cost basis, proceeds, fees, and what a profit figure doesn't capture.Investing
How "if I had invested" calculations work
Turning a past price and a hypothetical amount into an ending value.Options
The wheel options strategy, explained
Cycling between cash-secured puts and covered calls for premium income.Options
Option pricing and Black-Scholes explained
What drives a theoretical option price, and where the model breaks down.Loans
How a loan payment is calculated
The amortization formula behind every fixed monthly payment.Loans
EMI explained
Same formula as a loan payment, a different naming convention.Tax
How income tax is estimated
Taxable income, a flat rate, and credits — and what a real return adds.Financial planning
The financial health score, explained
Four weighted components, and why the weighting itself is a judgment call.Everyday maths
Percentage change, explained
Why the original value in the denominator changes everything.Everyday maths
Currency conversion, explained
A single multiplication, and why the rate you use matters.
Debt
How debt payoff time is calculated
A month-by-month simulation, and why payment size has a floor.Financial planning
How an emergency fund target is calculated
Essential expenses times a coverage window, minus what you already have.Retirement
The FIRE number, explained
Why a withdrawal rate assumption drives the entire target.Financial planning
How net worth is calculated
Assets minus liabilities, and why it's a snapshot, not a forecast.Financial planning
How monthly cash flow is calculated
Why positive net worth and negative cash flow can coexist.Everyday maths
The true cost of car ownership, explained
Why purchase price is one input out of four.Savings
How future education costs are estimated
Compounding a cost forward, the same way you'd compound a balance.Financial planning
How an insurance coverage gap is estimated
Years of income, plus debts, minus savings.Investing
How dividend income is calculated
Why yield and income answer two different questions.
Investing
Compound interest, contribution by contribution
How time, deposits and an assumed rate interact.
Options
How to read an options payoff graph
Profit, loss, breakeven and expiration risk in one frame.
Mortgages
What a mortgage payment estimate leaves out
Principal, interest, taxes, insurance and affordability assumptions.Retirement
A retirement balance is not retirement income
Why accumulation, spending and sequence risk are different questions.More guides
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