Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Average cost per share
$74.5000
Total shares
200
Total invested
$14,900.00
Current position value
$16,800.00
Unrealized gain/loss
$1,900.00
Return on the position
12.75%
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter buy 1 — price ($).
- 2Enter buy 1 — shares.
- 3Enter buy 2 — price ($).
- 4Enter buy 2 — shares.
- 5Enter buy 3 — price ($).
- 6Enter buy 3 — shares.
- 7Enter current price ($).
- 8Read your average cost per share on the right — it updates as you type.
- 9Hit Share to keep the scenario or send it to someone.
About this calculator
Averaging down lowers your break-even but raises your position size. Knowing the blended basis is the difference between a plan and hoping.
Worked example
Using the values the calculator loads with:
Inputs
- Buy 1 — price: 100 $
- Buy 1 — shares: 50
- Buy 2 — price: 78 $
- Buy 2 — shares: 50
- Buy 3 — price: 60 $
- Buy 3 — shares: 100
- Current price: 84 $
Results
- Average cost per share: $74.50
- Total shares: 200
- Total invested: $14,900.00
- Current position value: $16,800.00
- Unrealized gain/loss: $1,900.00
- Return on the position: 12.75%
What each field means
Inputs
- Buy 1 — price ($)
- The buy 1 — price used in the calculation, measured in $. Starts at 100 $ so you have a working example on load.
- Buy 1 — shares
- The buy 1 — shares used in the calculation. Starts at 50 so you have a working example on load.
- Buy 2 — price ($)
- The buy 2 — price used in the calculation, measured in $. Starts at 78 $ so you have a working example on load.
- Buy 2 — shares
- The buy 2 — shares used in the calculation. Starts at 50 so you have a working example on load.
- Buy 3 — price ($)
- The buy 3 — price used in the calculation, measured in $. Starts at 60 $ so you have a working example on load.
- Buy 3 — shares
- The buy 3 — shares used in the calculation. Starts at 100 so you have a working example on load.
- Current price ($)
- The current price used in the calculation, measured in $. Starts at 84 $ so you have a working example on load.
Results
- Average cost per share
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total shares
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total invested
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Current position value
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Unrealized gain/loss
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Return on the position
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the average cost basis calculator work?
Averaging down lowers your break-even but raises your position size. Knowing the blended basis is the difference between a plan and hoping. The underlying maths is: Average basis = Total invested ÷ Total shares.
What do I need to enter?
7 values: buy 1 — price, buy 1 — shares, buy 2 — price, buy 2 — shares, buy 3 — price, buy 3 — shares, and current price. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the average cost per share result mean?
It is returned as a money amount in US dollars and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Who is this tool for?
It's built for anyone comparing money scenarios before committing — budgeting a payment, sanity-checking a quote, or seeing what a change in rate or term actually costs.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Cost Basis Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/cost-basis
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/cost-basis" target="_blank" rel="noopener">Cost Basis Calculator — RevenueLab</a> (2026).</p>
Source: [Cost Basis Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/cost-basis) (2026).