Mark to market updates the recorded value of a position to what it would fetch in the market today. Trading books, derivatives, and many investment portfolios use this approach so gains and losses show up quickly. It improves transparency when prices are reliable, but it can add earnings volatility. When markets freeze, fair value becomes harder to observe and models fill the gap. Cost accounting, by contrast, keeps historical purchase prices until sale or impairment.

Key takeaways

  • MTM reflects current prices, not what you paid years ago.
  • It can make reported profit swing even if you have not sold.
  • Illiquid assets challenge pure mark to market valuation.
  • Know whether a figure is market based or cost based before you compare firms.