Stock Average Calculator
This Stock Average Calculator computes weighted average share price, updates averages after additional purchases or sales, and helps estimate target sell prices. It supports both aggregate totals and up to six detailed trade rows for flexible input.
Results assume the average-cost approach to cost basis unless you track lots (FIFO/LIFO). Use row entry or aggregate totals as appropriate. For tax reporting or lot-level profit calculations, consult your broker or tax advisor.
Governance
Record e7ba327a9f4b • Reviewed by Fidamen Standards Committee
Update your average price after buying additional shares. Uses weighted average (cost basis aggregated).
Inputs
Advanced inputs
Trade rows (up to 6)
Results
Updated average price
$10.18
Total shares after purchase
110
Total cost after purchase
$1,120.00
| Output | Value | Unit |
|---|---|---|
| Updated average price | $10.18 | USD |
| Total shares after purchase | 110 | shares |
| Total cost after purchase | $1,120.00 | USD |
Visualization
Methodology
The tool uses weighted-average arithmetic: average price = total cost / total shares. When adding purchases we sum prior cost and new cost, then divide by combined shares.
For sales, the calculator assumes the average-cost method where cost basis decreases proportionally; realized profit or loss is computed as shares sold × (sale price − average cost). Lot-level accounting (FIFO/LIFO) is outside this calculator's scope.
Key takeaways
Use aggregate mode when you have total shares and total cost. Use row entry for per-trade inputs. Use add-purchase to update average after a new buy, and use sale mode to compute realized P/L assuming average-cost basis.
This tool is not a substitute for broker lot reports or tax advice. For precise tax treatment, refer to your tax authority and broker statements.
Worked examples
Aggregate example: 150 shares total cost $1,650 → average = 1650 / 150 = $11.00 per share.
Add purchase example: hold 100 shares at $10, buy 50 shares at $12 → new average = (100×10 + 50×12) / 150 = $10.67.
Sale example: hold 100 shares at $10, sell 20 at $15 → realized profit = 20 × (15 − 10) = $100; remaining shares = 80 and average remains $10 under average-cost method.
F.A.Q.
Does this calculator handle FIFO or LIFO?
No. This calculator uses the average-cost approach. For FIFO/LIFO (lot-level) calculations you need transaction-level lot tracking and broker reports; consult your broker or tax advisor for lot-level realized P/L.
Are results exact for tax reporting?
Results are estimates based on the inputs and assumptions you select. Taxable gain/loss depends on jurisdictional rules, broker lot selection, fees, and applicable tax regulations. Consult a tax professional before filing.
Can I include transaction fees and commissions?
Yes. For accurate cost basis, add fees to the cost of the corresponding purchase (or subtract from sale proceeds). This calculator treats fees as part of cost when included in the inputs.
What rounding and precision does the calculator use?
Displayed values are rounded to two decimal places for prices and currency amounts. Underlying calculations use full precision; round-off may produce small differences.
Sources & citations
- NIST - National Institute of Standards and Technology — https://www.nist.gov
- ISO 31000 — Risk management — https://www.iso.org/iso-31000-risk-management.html
- IEEE standards (numeric computing and formats) — https://www.ieee.org
- OSHA — Occupational Safety and Health Administration — https://www.osha.gov
- SEC — Investor.gov Educational Resources — https://www.investor.gov/
- CFA Institute — Global Investment Performance Standards (GIPS) — https://rpc.cfainstitute.org/gips-standards
- FINRA — Investment Products — https://www.finra.org/investors/investing/investment-products
Further resources
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
Record ID: e7ba327a9f4bWhat changed (latest)
v1.0.0 • 2025-11-18 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Versioning & Change Control
Audit record (versions, QA runs, reviewer sign-off, and evidence).
What changed (latest)
v1.0.0 • 2025-11-18 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Public QA status
PASS — golden 25 + edge 120
Last run: 2026-01-23 • Run: golden-edge-2026-01-23
Engine
v1.0.0
Data
Baseline (no external datasets)
Content
v1.0.0
UI
v1.0.0
Governance
Last updated: Nov 18, 2025
Reviewed by: Fidamen Standards Committee (Review board)
Credentials: Internal QA
Risk level: low
Reviewer profile (entity)
Fidamen Standards Committee
Review board
Internal QA
Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person
Semantic versioning
- MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
- MINOR: New features or fields that do not change existing outputs for the same inputs.
- PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.
Review protocol
- Verify formulas and unit definitions against primary standards or datasets.
- Run golden-case regression suite and edge-case suite.
- Record reviewer sign-off with credentials and scope.
- Document assumptions, limitations, and jurisdiction applicability.
Assumptions & limitations
- Uses exact unit definitions from the Fidamen conversion library.
- Internal calculations use double precision; display rounding follows the unit's configured decimal places.
- Not a substitute for calibrated instruments in regulated contexts.
- Jurisdiction-specific rules may require official guidance.
Change log
v1.0.0 • 2025-11-18 • MINOR
Initial publication and governance baseline.
Why: Published with reviewed formulas, unit definitions, and UX controls.
Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 8afa65d599c9