Business Finance for Online Sellers

The mathematics
of true profit.

Free business and finance guides for online sellers, freelancers, and creators — the actual math behind platform fees, payment processing, self-employment taxes, insurance, and what you keep. Eight phases, from Create to Exit. No signup.

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How to make money online.

The boring answer

cash flow.

Understand how cash moves through an online business — platform fees, taxes, insurance, reserves, and what actually lands in your account.

From a new idea to a selling business. Read the guide for what you're doing right now. Follow the timeline below. Run the numbers. Move forward.

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Free simulation

Marketplace Lab

Run a multi-channel seller business in your browser — Amazon, eBay, Etsy, Walmart & Shopify. Fees, shipping, returns, delayed payouts, tax, insurance, and exit. No signup.

Launch the simulation
The Cash Flow Cycle

Eight phases.
One journey.

Every online business moves through the same eight phases, in the same order — from validating unit economics to planning your exit. Follow the timeline to see where you are, and what comes next.

01 Create

Find what's actually worth building — before you spend a dollar on inventory. Validate demand, test the economics, kill bad ideas early.

→ This is the cheapest phase — every phase after costs money.
02 Publish

Where you place the product changes what you keep. The platform decision, the listing, the storefront — this is where margin gets locked in or lost.

→ Placement decides your take-home per sale — before you list a single unit.
03 Deliver

Shipping, packing, returns — the operational layer that quietly decides whether you profit. Landed cost, return rates, packaging choices.

→ Every shipment, every return, every damaged box: all margin.
04 Earn

Income arrives — from ad revenue, sponsorships, affiliates, digital products, services, or client work. Most creators stack three or four of these.

→ Income enters. This is the top line — everything downstream works from here.
05 Profit

What's left after platform fees, cost of goods, refunds, and ad spend — the number that actually lands in your account. This is where you learn to run the real math.

→ Income minus costs. The number that lands in your bank — the only one that matters.
06 Protect

Buffer for slow months. Insurance for what could go wrong. Tax reserved before it's owed. The phase most creators skip — and the one that ends the ones who do.

→ Profit gets split. Some to buffer, some to tax, some to insurance — before you spend a thing.
07 Invest

Put the money to work — in markets, in retirement accounts, or back into the business. The math that turns a profitable year into lasting stability.

→ Money makes money. The whole point of getting here.
08 Exit

Realize the value you built — sell the store, transition to passive income, or close clean. The last chapter nobody writes about until they have to.

→ Capital becomes realized value. You walk away with what you built.
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And then a new cycle begins — same business refined, or something entirely new.
Common questions

Questions, answered.

What is JunctionKit?

JunctionKit is a free library of business and finance guides and calculators for people who sell online. Every guide is filed under one of eight lifecycle phases — Create, Publish, Deliver, Earn, Profit, Protect, Invest, and Exit — so you can find the material that matches whatever stage your business is actually in.

Who is JunctionKit for?

Online sellers, freelancers, solo founders, and ecommerce operators — anyone earning money independently who needs to handle platform fees, payment processing, self-employment taxes, contracts, and long-term money decisions without hiring an accountant or a lawyer for every question.

Is JunctionKit free?

Yes. Every guide and calculator on JunctionKit is free to read and use, with no account or signup required. The site is funded by display advertising and occasional affiliate links, which are disclosed in full on the disclosure page.

What topics does JunctionKit cover?

Platform fees and take-home rate math, payment processing and chargebacks, self-employment tax and reserves, business insurance, contracts and intellectual property, retirement accounts for self-employed operators, and business valuation. The eight-phase lifecycle runs from Create through Exit, covering both day-to-day operations and long-term planning.

Is JunctionKit financial advice?

No. JunctionKit publishes general educational information, not personalized financial, tax, or legal advice. The guides and calculators are built to help you understand how the money mechanics work — fees, taxes, insurance, contracts — so you can make informed decisions and have better conversations with a qualified professional when you need one.

The math behind
every sale.

Free guides, free calculators. No signup. No tracking. Just the numbers.

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