OmniTools

Average Down & Cost Basis Calculator

See your new average price after buying more, and how many shares a target average needs.

Basis: New average = (held × current average + added × buy price) ÷ total shares. The target back-solve is n = held × (target − average) ÷ (buy price − target)·2026-09-13 verified·Editorial policy

Before you rely on this

Your average can never fall below the price you buy at — a target under that is unreachable no matter how much you buy. Commissions, transaction taxes and currency conversion are excluded, and a lower average does not mean a smaller loss: adding to the same position increases the money at risk.

Tool Overview & Key Purpose

Works out your new average price after buying more, and how many extra shares a target average would take. It also states plainly the limit most averaging tools leave out: your average can never fall below the price you are buying at.

Step-by-Step Usage Instructions

1STEP 1

Enter the shares you hold and your current average price.

2STEP 2

Enter how many more you would buy and at what price — a limit price you are considering works fine.

3STEP 3

Add the market price to see unrealised profit and loss before and after the purchase, side by side.

4STEP 4

Enter a target average and the required share count is back-solved; if the target is unreachable it says so.

Real-World Scenarios & Practical Cases

3 Practical CasesScenario #1

Doubling up on a halved position

100 shares bought at 50, now at 30: buying another 100 at 30 brings the average to 40. Capital committed rises from 5,000 to 8,000 and the break-even price falls from 50 to 40.

The average drops but the loss does not — you simply have more money moving on the same percentage swing.Scenario #2

Setting a target average

In that same position, getting the average down to 35 takes 300 more shares at 30 — about 9,000, close to double the original investment.

Every further step down costs disproportionately more shares. Back-solving makes that steepness visible.Scenario #3

Spotting an impossible target

With an average of 50 and a buy price of 30, a target of 25 has no answer: no quantity bought at 30 can pull the average below 30.

A target only exists if it sits above the price you are buying at.Weighted average price formula

New average = (held × current average + added × buy price) ÷ (held + added)
Shares needed for a target: n = held × (target − average) ÷ (buy price − target)
When the denominator is zero or negative there is no answer — the target sits at or below the price you are buying at.

Pro Tips & Key Considerations

A lower average is not a smaller loss. Read it next to the "before" percentage shown on screen.Commissions and transaction taxes are excluded; buying in many small lots makes them visible in the real average.Repeatedly adding to a falling position also concentrates your portfolio. Check the position size before the price.

Frequently Asked Questions (FAQ)

Sources & References

Investopedia — "Averaging Down" definition U.S. SEC Investor.gov — "Cost Basis" glossary entry

Basis: New average = (held × current average + added × buy price) ÷ total shares. The target back-solve is n = held × (target − average) ÷ (buy price − target) · 2026-09-13 verified