How much is using market orders instead of limit orders actually costing me over time?

How this is calculated

• Extra slippage per share equals your market-order slippage minus your limit-order slippage. If limit orders cost more in what you entered, extra cost is treated as zero.
• Extra cost per trade equals that extra slippage per share multiplied by your average shares per trade. Monthly cost multiplies that by your trades per month, and total cost multiplies monthly cost by your time horizon.
• This model does not account for missed fills. Limit orders can go unfilled while price runs away, which has its own cost that this tool does not attempt to estimate.
• Your slippage inputs are estimates you supply, ideally pulled from your own broker execution reports or a recent bid-ask spread. This tool does not fetch live spread data.
• The point of this simulator is to make an easy-to-ignore, per-trade cost visible at the scale it actually happens: across a month or a year of trades, not one trade at a time.