johnnyji.dev

Practical calculators for traders and builders.

Estimate average entry prices, fee-adjusted break-even levels, position size, API usage, and side project run rates. Each tool includes the formula, an example, and the assumptions that matter before you rely on the number.

Built For

  • Fast calculators that work without an account.
  • Plain-language explanations for every formula.
  • Risk and cost notes that make hidden assumptions visible.

Tools

Start with a number you can act on

These calculators are educational planning tools. They do not provide financial, tax, legal, or investment advice.

Average Entry

Calculate the weighted average entry price after multiple buys. This is useful when you add to a spot position or average into a trade over time.

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DCA Plan

Plan a dollar-cost averaging sequence before you place orders. Estimate how a new set of buys changes your average entry, total exposure, and cash required.

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Break-Even

Estimate the exit price needed to cover entry and exit fees. This helps you avoid mistaking a small gross gain for a net profit.

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Position Size

Calculate position size from account balance, risk percentage, entry price, and stop price. This turns a risk rule into a concrete order size.

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API Cost

Estimate monthly API spend from request volume, token usage, or metered unit pricing. Use it before launching a side project or automation job.

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Project Cost

Estimate the monthly operating cost of a side project by combining hosting, database, storage, API, email, analytics, and miscellaneous tools.

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Guides

DCA vs Grid Trading

A practical comparison of dollar-cost averaging and grid trading for builders who automate trading workflows.