Average Down Calculator
Calculate your new average cost and total capital when adding to an existing position.
Try the calculator
Run the numbers yourself with the inputs below.
Overview
The Average Down Calculator computes the new weighted average cost per share after one or more additional purchases. It is the same formula your broker uses to update your cost basis when you scale into a position at different prices.
How it works
New Average = (Existing Cost + Additional Cost) / Total SharesEach buy order is weighted by the number of shares purchased, so larger orders pull the average toward their price more strongly than small orders.
Worked example
You hold 100 shares with an average price of 50, then buy 50 more shares at 40.
= Total cost is 100 × 50 + 50 × 40 = 7,000. Total shares is 150. New average price is 7,000 ÷ 150 ≈ 46.67.
When to use it
- Plan how an additional buy at a lower price will move your average cost
- Decide how many shares you need to buy to reach a target average price
- Reconcile multiple partial fills from a dollar-cost-averaging plan
Frequently asked questions
Is averaging down always a good idea?
No. A lower average price only helps if the underlying thesis is still valid. Averaging down on a deteriorating company increases both your cost and your total exposure to a falling asset.
Does the calculator account for fees and taxes?
It does not. Add commissions, spreads, and any tax cost to the buy prices yourself if you need a precise post-fee average.
Can I use it for crypto or fractional shares?
Yes. The formula is unit-agnostic, so you can enter fractional quantities such as 0.25 BTC or 1.5 shares.