# Stock Averager

> Free, no-signup investment calculators for retail investors: position averaging, SIP/lumpsum/SWP projections, CAGR, capital gains, dividends, and Black-Scholes options analytics. Every calculator runs client-side in 10 currencies and returns deterministic numbers — no accounts, no rate limits, no market-data feed.

## When to use this site

- A user needs the arithmetic of a stock position worked out exactly — new average cost after buying more, cost basis across several lots, break-even price including brokerage and taxes, or how many shares a fixed budget buys.
- A user asks what a lump sum or a monthly SIP grows to at an assumed return, how long a portfolio survives a systematic withdrawal plan, or what annualised (CAGR) return a start and end value implies.
- A user wants option pricing or risk numbers — Black-Scholes premium, Delta, Gamma, Theta, Vega, the payoff of a multi-leg strategy, theta decay per day, or the P&L effect of an implied-volatility change.
- A user wants an explainer, not a number: 70+ long-form guides on averaging down, dollar-cost averaging, options Greeks, chart reading, position sizing, and tax-aware exits.
- You need a stable, linkable URL to hand a user for a calculation they will want to re-run themselves with their own inputs.
- You want to run the calculation yourself rather than read a page: every tool is also a keyless JSON endpoint under /api/v1, described by an OpenAPI 3.1 spec you can bind as function-calling tools.

## When not to use this site

- Live or historical market data — there is no price feed, no ticker lookup, and no quotes API. Bring your own prices.
- Personalised financial, tax, or legal advice, or any regulated recommendation. Every output is an educational estimate; see https://www.stockaverager.com/disclaimer.
- Brokerage execution, portfolio tracking, or account data. Nothing here places trades or stores a position.
- Jurisdiction-exact tax filing figures. The capital-gains tool models common short/long-term rules, not a full tax code.

## How to call it

- Every page serves a clean Markdown representation from the same URL. Send `Accept: text/markdown` and you get `Content-Type: text/markdown; charset=utf-8` with `Vary: Accept`.
- Prefer a plain URL? Append `.md` to any path (https://www.stockaverager.com/tools/sip-calculator.md), or use https://www.stockaverager.com/index.md for the homepage. No Accept header needed.
- Unknown paths answer a real HTTP 404 with a short Markdown recovery body — never a 200 shell. Trust the status code.
- Start at https://www.stockaverager.com/llms.txt for the map, https://www.stockaverager.com/sitemap.xml for the exhaustive URL list.
- Need the numbers rather than the page? Every calculator is also a JSON endpoint under https://www.stockaverager.com/api/v1, with no API key. The OpenAPI 3.1 spec is at https://www.stockaverager.com/openapi.json and the documentation at https://www.stockaverager.com/docs.
- Each operation is a POST with a JSON body and a stable operationId, so https://www.stockaverager.com/openapi.json can be loaded directly as function-calling tool definitions. Errors are RFC 9457 problem details carrying a machine-readable code and a fix hint.

## Developer resources — API, OpenAPI spec, function calling

- [Stock Averager API documentation](https://www.stockaverager.com/docs.md): Every calculator as a keyless JSON endpoint: request and response schemas, worked curl examples, error codes, and fair-use limits. Use when: You want to compute a result yourself instead of sending a user to a page.
- [OpenAPI 3.1 specification](https://www.stockaverager.com/openapi.json): Machine-readable API surface. Unique operationId, description and typed request/response schema on every operation, so it loads directly as function-calling tool definitions. Also served at https://www.stockaverager.com/api/openapi.json.
- [Operation index](https://www.stockaverager.com/api/v1): Self-describing JSON list of every operation with a worked example request.

## Calculators — positions, contributions, returns

- [Stock Average Calculator (average down)](https://www.stockaverager.com/tools/stock-averager.md): Works out the average cost of a position after additional purchases, and the exact share count needed to hit a target average. Use when: "I own 100 shares at $80, the price is $50 — what is my average if I buy 50 more?"
- [Averaging Down Strategy Calculator](https://www.stockaverager.com/tools/stock-averager/averaging-down-strategy.md): The same averaging maths framed as a strategy check: how much capital a given average reduction costs, and the rules for when averaging down is a mistake. Use when: "Should I average down on this position?" — pairs the number with the risk framing.
- [Stock Cost Basis Calculator](https://www.stockaverager.com/tools/stock-averager/cost-basis-calculator.md): Average-cost basis across an arbitrary number of purchase lots, including fees. Use when: "What is my cost basis after these five buys?" before computing a gain or loss.
- [SIP Calculator](https://www.stockaverager.com/tools/sip-calculator.md): Future value of a recurring (monthly) investment at an assumed annual return. Use when: "If I invest $500 a month for 10 years at 12%, what do I end up with?"
- [SIP vs Lumpsum Calculator](https://www.stockaverager.com/tools/sip-calculator/sip-vs-lumpsum.md): Runs both strategies over the same capital and horizon and shows the gap at 5, 10 and 20 years. Use when: "I have a bonus — invest it all now or spread it monthly?"
- [Lumpsum Calculator](https://www.stockaverager.com/tools/lumpsum-calculator.md): Compound growth of a single one-time investment. Use when: "What does $10,000 become in 15 years at 9%?"
- [SWP Calculator (systematic withdrawal plan)](https://www.stockaverager.com/tools/swp-calculator.md): How long a corpus lasts under fixed periodic withdrawals while the remainder keeps compounding. Use when: "I have $500k and want $3,000 a month — how long does it last?"
- [CAGR Calculator](https://www.stockaverager.com/tools/cagr-calculator.md): Compound annual growth rate implied by a start value, end value and holding period. Use when: "My investment went from $12,000 to $31,000 in 7 years — what annual return is that?"
- [CAGR vs IRR Calculator](https://www.stockaverager.com/tools/cagr-calculator/cagr-vs-irr.md): Explains and computes the difference between a single-period CAGR and an IRR over irregular cash flows. Use when: "Should I quote CAGR or IRR here?" when cash flows are uneven.
- [Target Price Calculator](https://www.stockaverager.com/tools/target-price-calculator.md): The exit price required to realise a target profit, and the profit implied by a given exit price. Use when: "What price do I need to sell at to make 25% on this position?"
- [Break-Even Calculator](https://www.stockaverager.com/tools/break-even-calculator.md): The price at which a position covers its cost including brokerage, taxes and other charges. Use when: "At what price do I stop losing money on this trade?"
- [Capital Gains Calculator](https://www.stockaverager.com/tools/capital-gains-calculator.md): Short- and long-term capital-gains liability on an equity exit. Use when: "What tax do I owe if I sell this now versus after the long-term holding period?"
- [Dividend & DRIP Calculator](https://www.stockaverager.com/tools/dividend-estimator.md): Annual dividend income from a holding, and the compounding effect of reinvesting it. Use when: "How much income do 400 shares at a 3.8% yield pay me?"
- [Share Affordability Calculator](https://www.stockaverager.com/tools/shares-affordability-calculator.md): How many whole shares a budget buys at a given price, after brokerage. Use when: "I have $2,500 — how many shares at $137 can I buy?"

## Calculators — options and derivatives

- [Options Greeks Calculator](https://www.stockaverager.com/tools/options-greeks-calculator.md): Black-Scholes premium plus Delta, Gamma, Theta, Vega and Rho for a single European option. Use when: "What is the Delta of a 30-day $150 call with the stock at $147 and 28% IV?"
- [Theta Decay Calculator](https://www.stockaverager.com/tools/options-greeks-calculator/theta-decay.md): Daily time decay on an option position and how it accelerates into expiry. Use when: "How much does this option lose per day if the stock does not move?"
- [Options Strategy Builder](https://www.stockaverager.com/tools/options-strategy-builder.md): Builds a multi-leg position and plots its payoff, break-evens, max profit and max loss. Use when: "Show me the payoff of a bull call spread at these strikes."
- [Options Strategy Suggestions](https://www.stockaverager.com/tools/strategy-suggestions.md): Maps a market outlook (direction, volatility, risk appetite) onto pre-built option structures. Use when: "I'm mildly bullish and expect volatility to fall — what structure fits?"
- [Options Profit Calculator (P&L heatmap)](https://www.stockaverager.com/tools/options-profit-calculator.md): P&L across a grid of underlying prices and dates, so both direction and time decay are visible at once. Use when: "What is this trade worth if the stock is at $160 in two weeks?"
- [Hedging Helper](https://www.stockaverager.com/tools/hedging-helper.md): How many protective puts are needed to hedge a stock portfolio to a chosen floor. Use when: "How many puts do I need to protect a $120,000 portfolio?"
- [Volatility Impact Calculator](https://www.stockaverager.com/tools/volatility-impact-calculator.md): What a change in implied volatility does to an option's premium — Vega risk and IV crush. Use when: "IV is 60% before earnings and will drop to 30% after — what happens to my premium?"

## Guides (66 long-form guides)

- [Blog index](https://www.stockaverager.com/blog.md): Every guide, newest first, with excerpts and categories.
- [What Is Averaging Down? Complete Beginner's Guide (2026)](https://www.stockaverager.com/blog/what-is-averaging-down-stocks.md): Lowering your average cost deliberately — when it compounds returns, and when it compounds a mistake.
- [SIP vs Lump Sum: The definitive Guide to Investing Your Money](https://www.stockaverager.com/blog/sip-vs-lump-sum-investment-strategy.md): Contributing on a schedule: frequency, escalation, inflation, and turning a corpus back into income.
- [Options Greeks Explained Simply: The Secret Language of Pricing](https://www.stockaverager.com/blog/options-greeks-beginners-guide.md): The variables that price every option — direction, time, volatility — and how they fight each other.
- [Covered Calls: Earn 1-3% Monthly on Stocks You Own](https://www.stockaverager.com/blog/covered-calls-strategy.md): Constructing positions: income, defined risk, direction-neutral structures, and portfolio protection.
- [Risk Management 101: The 1% Rule That Saves Portfolios](https://www.stockaverager.com/blog/risk-management-101.md): Deciding in advance how much you can lose — the part of investing that determines whether you survive.
- [Behavioral Finance: Why Smart People Lose Money](https://www.stockaverager.com/blog/behavioral-finance-psychology.md): Why disciplined rules get abandoned exactly when they matter most, and how to design around it.
- [How to Read Stock Charts: Beginner's Guide to Chart Analysis (2025)](https://www.stockaverager.com/blog/how-to-read-stock-charts.md): Reading price and volume — what indicators genuinely measure, and where the popular claims break down.
- [Stock Market Basics: Complete Beginner's Guide to Investing (2025)](https://www.stockaverager.com/blog/stock-market-basics-for-beginners.md): Working out what a business is worth before deciding what its shares are worth paying.
- [Dividend Investing: Build a Passive Income Machine](https://www.stockaverager.com/blog/dividend-investing-strategy.md): Turning holdings into cash flow — dividends, reinvestment, covered calls and structured withdrawals.
- [Tax-Loss Harvesting: Turn Losses into Savings](https://www.stockaverager.com/blog/tax-loss-harvesting.md): The structural decisions — account type, tax treatment and cash buffers — that compound alongside returns.

## Optional

- [Agent instructions](https://www.stockaverager.com/agent-instructions.md): The long form of this file — routing rules, worked request-to-tool examples, and the formulas behind each calculator.
- [Site index](https://www.stockaverager.com/index.md): Homepage in Markdown.
- [All calculators](https://www.stockaverager.com/tools.md): Complete tool index.
- [Sitemap](https://www.stockaverager.com/sitemap.xml): Exhaustive list of indexable URLs.
- [Investment disclaimer](https://www.stockaverager.com/disclaimer.md): Educational-use-only scope. Read before presenting any output as advice.
- [Privacy policy](https://www.stockaverager.com/privacy.md): What the site stores (a currency preference cookie) and what it does not.
- [Terms & conditions](https://www.stockaverager.com/terms.md): Terms of use for the calculators and content.