Mark price vs last price: which one is your option really worth?
The last price is the price of the most recent trade, which on a quiet option can be days old. The mark price is usually the midpoint of the current bid and ask. When your P/L jumps for no reason, a stale last price is often why.
The short answer
Trust the mark to see what an option is worth now. Trust the ask (to buy back) or the bid (to sell) to see what it would cost to close. Never trust the last price on its own.
The last price is just the most recent trade. Most options trade far less often than stocks. A strike can go hours or days with no trade, so its last price can be stuck at a level from a different market.
The Mark price is usually the halfway point between the Bid price and the Ask price, refreshed all day. Brokers can calculate it a little differently, so check what yours uses on its help page.
Side by side
| Last price | Mark price | |
|---|---|---|
| What it is | The price of the latest trade | Usually the midpoint of bid and ask |
| How fresh | As old as the last trade, maybe days | Updates with every quote |
| On a busy option | Close to the mark | Close to the last |
| On a quiet option | Can be far off | Still tracks today's market |
| Used for P/L by | Some apps and some screens | Most brokers' P/L and account values |
| Can you trade at it? | Not unless the market comes back there | Sometimes, with a patient limit order |
A worked example (hypothetical)
You sold one put on a made-up stock, Pine Valley Energy, for $2.00 ($200). Three days ago the stock dipped for an hour, and one trade in your put printed at $3.50. Nobody has traded that strike since. The stock has recovered.
Today's quote is $1.70 bid, $1.90 ask. The mark is the middle: $1.80.
| Price you look at | Value of the put | Your P/L on the short put |
|---|---|---|
| Last price ($3.50, three days old) | $350 | ($2.00 − $3.50) × 100 = −$150 |
| Mark ($1.80) | $180 | ($2.00 − $1.80) × 100 = +$20 |
| Ask ($1.90): what you'd pay to buy it back now | $190 | ($2.00 − $1.90) × 100 = +$10 |
Same position, same minute, three answers. If your app shows the last price, you see a $150 loss on a trade that's slightly ahead. If you panic and close, you pay the ask, about $1.90, and the "loss" was never real.
It can fool you the other way too. A last price stuck low after a quiet week can make a short option look like a winner while the real ask has climbed. Then the bill shows up when you try to close.
When the P/L moves and the stock didn't, check the time of the last trade before you check anything else.
Why the last price goes stale
A popular stock trades many times a second. An option on it might trade a few times a day, and a far strike a few times a week. The chain still shows a "last" for every strike, with no warning about age. Most platforms show the trade time if you open the quote; look for it.
The mark has its own weak spot. On a quiet strike, the bid and ask can be far apart, so the midpoint is a guess. A $1.00 bid and a $3.00 ask make a $2.00 mark, but you may never fill there. See mid price vs natural price for how to work an order in a wide market.
Which number should you use?
| Use the mark if… | Use the bid or ask if… | Use the last if… |
|---|---|---|
| You want a fair value right now | You're about to close the trade | The trade time is seconds old |
| You track P/L day to day | You set a limit price | You check what really traded |
| The spread is tight | The spread is wide | Never as a value on its own |
Set alerts and stop prices on the stock or on the mark, not on the last trade. A stop that fires on a stale print is a common way to give away money; see stop loss on options vs a mental stop.
For a seller running the wheel strategy, the mark is the number to track, and the ask is the number you pay to buy back. The options strategy comparison chart puts the bigger choices side by side. The options quote guide explains each column on the chain.
Questions
What is the difference between mark price and last price?
The last price is the most recent trade, however old. The mark is usually the midpoint of the current bid and ask. On a quiet option the two can be far apart, and the mark is the better guide.
Why did my option P/L jump when the stock didn't move?
Often a stale last price, or a bid-ask spread that widened. Check the trade time on the last price and the size of today's spread. The mark and the ask tell you what the option is worth now.
Does my broker use the mark or the last price for P/L?
Most brokers value options at the mark, but not all, and some apps let you switch. Check your broker's help page or the settings on the positions screen.
Can I close my option at the mark price?
Sometimes. A limit order at the mark often fills on busy options if you're patient. On a wide, quiet market you may have to move toward the bid or ask.
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