Finance📅 12 March 2025⏱ 5 min read
How to Understand and Calculate Options Premium
An options premium has two components: intrinsic value and time value. Here is how each is calculated, what the Greeks mean in plain terms, and how to think about options pricing.
JW
James WhitfieldPersonal Finance & Maths WriterJames has written about personal finance, health metrics, and everyday mathematics for over six years. He holds a BSc in Mathematics from the University of Leeds.
Options pricing seems complex, but the core components are understandable without advanced maths. Understanding what you are actually paying for — and what drives price changes — is essential before trading options.
Options Premium = Intrinsic Value + Time Value
Premium = Intrinsic Value + Time Value (Extrinsic Value)
Intrinsic Value (IV): the in-the-money amount
For a CALL option:
IV = max(0, Stock Price - Strike Price)
For a PUT option:
IV = max(0, Strike Price - Stock Price)
Example: CALL option, strike price £50, stock at £55:
IV = max(0, 55 - 50) = £5
Example: PUT option, strike price £50, stock at £43:
IV = max(0, 50 - 43) = £7
If the option has zero intrinsic value, it is "out of the money":
CALL with strike £60, stock at £55: IV = max(0, 55-60) = £0
Time Value
Time Value = Premium - Intrinsic Value
Time value reflects:
- Time remaining to expiry (more time = more value)
- Implied volatility (more uncertainty = more value)
- Interest rates and dividends (minor effects)
CALL option: strike £50, stock £55, premium £7.50:
Intrinsic value: £5
Time value: £7.50 - £5.00 = £2.50
Out-of-the-money CALL: strike £60, stock £55, premium £1.20:
Intrinsic value: £0
Time value: £1.20 (entirely time value / extrinsic)
Time value decay (Theta):
Time value erodes as expiry approaches.
An option with 30 days to expiry loses time value faster than one with 6 months.
The decay accelerates in the last 30 days -- this is Theta decay.
The Greeks: What They Mean Practically
Delta: how much the premium changes per £1 move in the underlying
CALL Delta: 0 to 1 (deep in-the-money ≈ 1, deep out-of-the-money ≈ 0)
PUT Delta: -1 to 0
Delta 0.5: premium changes £0.50 for every £1 move in stock
At-the-money options are approximately 0.5 delta.
Theta: daily time value decay in pounds
Option with Theta -0.05: loses £0.05 per day just from time passing
30-day option might have Theta -£0.08/day; 5-day option: -£0.25/day
Vega: sensitivity to implied volatility changes
High Vega = option is expensive when volatility spikes
Options on volatile stocks (earnings announcements) have high Vega -- and premiums to match
IV crush: after earnings, implied volatility drops sharply
Options that seemed cheap before earnings often collapse in value post-announcement
Why Most Retail Traders Lose on Options
Buying out-of-the-money calls ("lottery tickets"):
Need stock to move significantly AND fast enough to overcome Theta decay.
A 30-day, 10% out-of-the-money call:
Requires approximately 15-20% move just to break even on expiry
Probability of profit: typically 20-30%
The math favours option sellers:
Time value always erodes to zero; sellers collect this decay.
Professional options traders typically sell premium, not buy it.
Beginner mistake: buying cheap out-of-the-money options
"Cheap" in price = very low probability of being in the money at expiry