Calculators

Each one runs the same formula as the article it came from, in your browser. Nothing you type is sent anywhere, nothing is stored, and there is no sign-up. Every result is an illustration on the stated assumptions, not advice.

• Margin call calculator
  P_call = loan per share ÷ (1 − maintenance rate)
  Find the exact price and percentage drop that triggers a maintenance margin call on a long position.
• Expense ratio drag calculator
  net balance = P × (1 + r − e)^n vs gross balance = P × (1 + r)^n
  See how much of your final balance an annual fund fee takes over a holding period, in dollars and as a share of the gross result.
• Position size calculator
  shares = (account × risk %) ÷ (entry − exit level)
  Work out the share count that keeps a single trade inside a fixed percentage of your account if the exit level is reached.
• Roth vs Traditional break-even calculator
  Roth = C × (1 − t_now) × (1 + r)^n · Traditional = C × (1 + r)^n × (1 − t_later)
  Compare after-tax outcomes for a Roth and a Traditional contribution, and find the retirement tax rate where they tie.

Why these four

They cover the questions where getting the arithmetic wrong costs the most: how far a leveraged position can fall before the broker sells it, what a fund fee actually removes over a working life, how large a position can be before one idea dominates the account, and which retirement account wins at your two tax rates. The reasoning behind each sits in the articles.