Guides
The detail behind each calculator — how the numbers are built, why the fees apply, and how to improve your result.
How your mortgage payment is calculated (and how to lower it)
Understand every part of your monthly mortgage payment — principal, interest, taxes, insurance, and PMI — with the amortization formula and ways to pay less.
Read the guideHow long to pay off a loan — and how extra payments help
See how payoff time and total interest are calculated, why minimum payments trap you, and how much extra payments save on credit cards and loans.
Read the guideWalmart Marketplace fees explained: a 2026 seller guide
A clear breakdown of Walmart Marketplace seller fees — the 6–15% category referral fee, no monthly cost, and WFS — with a worked example and ways to keep more profit.
Read the guideMargin vs markup: the difference that quietly wrecks pricing
Margin and markup are not the same number. Learn how to calculate each from cost and price, why a 50% markup is only a 33% margin, and how to price for a target margin.
Read the guideHow car loans work: payments, interest, and the term trap
Understand how auto loans work — what sets your monthly payment, how sales tax and fees are financed, and why a longer term quietly costs you more.
Read the guideAmazon FBA profit explained: how to find your real margin and ROI
Amazon FBA fees explained for 2026: referral rates by category, fulfilment fees by size tier, storage, returns and ads — and the real profit, margin and ROI.
Read the guideEtsy fees explained: how to work out your real profit per sale
Etsy fees explained for 2026: the 6.5% transaction fee really costs 9.6–14% once listing and payment fees land. Effective rates, worked examples, eBay comparison.
Read the guideTikTok Shop fees explained: what sellers really pay in 2026
TikTok Shop fees in 2026: the 6% referral fee, what you net on $10 to $500 orders, creator commissions, ads, returns, and how it compares to eBay and Amazon.
Read the guidePayPal fees explained: how much does PayPal really take?
PayPal fees explained for 2026: the 2.99% + $0.49 US rate, what you net on $10 to $10,000, micropayments, cross-border costs, refunds and how to pay less.
Read the guideShopify fees explained: how to calculate your real profit per sale
A plain-English breakdown of every Shopify fee — subscription, payment processing, and transaction fees — with worked examples and ways to pay less.
Read the guideHow to set your freelance rate (so the math actually works)
Freelance rate math for 2026: why salary ÷ 2,080 fails, the correct derivation, required rates at $50k–$200k, self-employment tax, day rates and rush fees.
Read the guideHow compound interest works (and how to use this calculator)
Understand compound interest — the formula, how monthly contributions grow, and why starting early matters most — with worked examples you can reproduce.
Read the guideHow to pay off credit card debt (and escape the minimum-payment trap)
Understand how credit card payoff works, why minimum payments keep you in debt for years, and how a higher fixed payment slashes your interest and timeline.
Read the guideHow to reach a savings goal (and how interest speeds it up)
Learn how a starting balance, monthly contributions, and interest combine to hit a savings goal — and which lever shortens the timeline the most.
Read the guideMortgage refinance: how to find your break-even point
How to calculate a mortgage refinance break-even point, when refinancing is worth it, and why a lower payment can still cost more over the life of the loan.
Read the guideHow to convert a salary to an hourly rate (and back)
Learn how to convert an annual salary to an hourly rate, what to factor in like PTO and benefits, and how to compare salaried and hourly job offers fairly.
Read the guideHow to calculate ROI (and why annualized return matters more)
Learn how to calculate return on investment, the difference between total ROI and annualized return, and why annualized is the fairer way to compare investments.
Read the guideHow retirement savings grow: contributions, match, and time
See how 401(k) savings grow from contributions, employer match, and compounding — and why starting early and capturing the full match matter most.
Read the guideHow to calculate percentages (the easy way)
Percentage calculator guide: every formula with worked examples — percent of a number, increase, decrease, percentage change, reverse percentages and error.
Read the guideHow VAT works: adding and removing value-added tax
VAT explained for 2026: add VAT by multiplying by 1.20, remove it by dividing by 1.20, plus UK and EU rate tables, the £90,000 threshold and reclaim rules.
Read the guideHow sales tax works (and how to calculate it)
US sales tax explained for 2026: combined state and local rates, how to calculate tax on any price, back tax out of a total, plus nexus and marketplace rules.
Read the guideHow your take-home pay is calculated (2026)
Understand how your paycheck is calculated in 2026 — federal income tax brackets, Social Security, Medicare, pre-tax deductions, and state tax — step by step.
Read the guideSelf-employment tax explained (2026)
Understand the 15.3% self-employment tax — how it’s calculated on 92.35% of net earnings, the Social Security and Medicare split, and the deductible half.
Read the guideHow to calculate your break-even point
Learn how to calculate a break-even point using contribution margin, with a worked example, the difference between fixed and variable costs, and ways to lower it.
Read the guidePoshmark fees explained: what you really keep per sale
A clear breakdown of Poshmark’s seller fees — the flat $2.95 under $15 and 20% above — with a worked example and tips to keep more of each sale.
Read the guideBreakeven ROAS explained: the number every ad campaign needs
What breakeven ROAS means, the exact formula, how to work out your target ROAS and maximum CPA, and the mistakes that make advertisers scale losing campaigns.
Read the guideStripe fees explained: what you really pay and what you keep
Every Stripe fee for 2026: the 2.9% + $0.30 base rate, international card and currency conversion surcharges, disputes, payouts, and how to work out your true net.
Read the guideWise vs PayPal vs Payoneer: which one actually pays you more?
A side-by-side comparison of Wise, PayPal, and Payoneer fees for freelancers — including the exchange-rate markup each one hides, with real numbers on a $2,000 payment.
Read the guideLanded cost explained: what imported inventory really costs you
How to calculate landed cost for imported inventory: freight, customs duty, CIF vs FOB, insurance, brokerage, and the per-unit number your pricing should actually be based on.
Read the guideWhat a discount really costs: promotion margin explained
Why a 30% discount can cost half your profit, how many extra sales a promotion needs to be worth running, and the deepest discount your margins can actually survive.
Read the guideMarketplace fees compared: where sellers actually keep the most
A 2026 marketplace fee comparison on one identical order: Shopify, Etsy, eBay, Amazon, Walmart, TikTok Shop, Poshmark and PayPal ranked by what you actually keep.
Read the guideRestocking fees explained: what you actually get refunded
What a restocking fee is, typical rates by category, whether restocking fees are legal, what Amazon, eBay and Best Buy charge, and how much of your refund survives.
Read the guideAmazon ROI explained: the number that beats margin
Amazon ROI calculator guide: the exact formula, a worked FBA example, ROI vs margin, inventory turns, benchmarks by sourcing model and break-even selling price.
Read the guideeBay fees explained: how to calculate your real profit per sale
eBay fees explained for 2026: the 13.25% final value fee, the $0.40 per-order fee, category rates, Store costs and ad rates — with take-home figures from $10 to $10,000.
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