Cash-Secured Put
Prerequisite strategies: you should already have bought and closed a long put, and read UK options basics and assignment and expiry. You are selling the instrument you have just learned to buy.
Why this structure exists
The problem this solves is ordinary. You want to own a share, but not at today's price. The obvious answer is a limit buy order below the market: you wait, and you are paid nothing for waiting. A cash-secured put is the same waiting with a fee attached. You sell someone the right to sell you 1,000 shares at your chosen price, set aside the full cash to honour it, and are paid a premium on the day you take the obligation on.
Two outcomes, and you must be content with both before you place it. Either the share stays above your strike and you keep the premium, or it falls through and you buy the shares you said you wanted at the price you said you wanted, with the premium reducing what you paid. What you give up is the upside: if the share runs away, the premium is all you get.
Why not just use a limit order and a savings account? Because the limit order pays you nothing for risk you are already carrying. The put pays you — but only if the premium beats the interest that cash earns elsewhere, which on a low-volatility UK share is a close call. The worked example runs that comparison in pounds.
Construction
| Leg | Buy / Sell | Quantity | Strike rule | Expiry rule | Target delta | Typical price |
|---|---|---|---|---|---|---|
| Put | Sell to open | 1 contract = 1,000 shares (ICE UK single stock) | A price you would be content to own at, 3–8% below spot | 30–45 days, monthly series, third Friday | −0.15 to −0.30 | 2–6p per share on a large FTSE 100 name |
| Cash | Set aside | Strike × 1,000 | Unencumbered until expiry or assignment | Released at expiry, or converted to shares | n/a | £4,000–£6,000 on a 400–600p share |
| Net | Net credit | One obligation, fully cash-covered | Constraint: cash set aside ≥ strike × contract size, at all times, with no other claim on it. If that inequality fails, this is not a cash-secured put — it is a naked short put wearing the wrong name. | |||
Contract size is the number nearly every online guide gets wrong for a UK reader. ICE Futures Europe publishes its UK single-stock options as rights over 1,000 shares, physically delivered, quoted in pence per share, tick 0.25p worth £2.50, American exercise, last trading day 16:30 London on the third Friday. ICE also launched newer standard and mini series from December 2025 in different sizes, so read the specification for your exact series. A US-listed option is 100 shares. A FTSE 100 index option is £10 per index point, cash-settled and European — it cannot deliver shares, so it cannot be used here.
The numbers before you click
Formulae: max profit = premium − costs. Max loss = (strike × contract size) − net premium, realised only if the share reaches zero. Breakeven = strike − premium + costs per share. Capital = strike × contract size. Figures are from the worked example below, not generic.
Entry criteria
| Gate | Rule | Why |
|---|---|---|
| Underlying | A FTSE 100 company you would hold for three years with no option attached | Assignment is the eventual outcome; you must want the shares |
| Implied volatility | Sell only at IV rank above 30. Below 25, do not sell | The premium stops paying for the risk |
| DTE window | 30–45 days, monthly series only | Steepest decay, with time to react |
| Strike / delta | Delta −0.15 to −0.30, at a price you would pay in cash today | Roughly a 70–85% chance of expiring worthless |
| Liquidity | Bid-ask no wider than 10% of mid; open interest above 100 | ICE UK chains are far thinner than US chains; the spread is a real cost |
| Event calendar | No results and no ex-dividend date inside the window | Both are scheduled steps down for a put seller |
Do not enter if: the cash is earmarked for anything else; you would not buy the shares outright at the strike today; the premium only looks generous because the company is in the news; the bid-ask is wider than the premium; or you cannot state the maximum loss in pounds from memory.
Greeks at entry and how they evolve
| Greek (seller's sign) | At entry, 32 DTE, 454p | 16 DTE, price unchanged | 7 DTE, price unchanged | 16 DTE after +1 SD (484p) | 16 DTE after −1 SD (424p) |
|---|---|---|---|---|---|
| Delta | +0.18 | +0.11 | +0.03 | +0.00 | +0.57 |
| Gamma (delta per 10p) | −0.09 | −0.09 | −0.05 | −0.00 | −0.16 |
| Theta | +£1.12/day | +£1.16/day | +£0.73/day | +£0.02/day | +£2.79/day |
| Vega (per +1 vol point) | −£3.52 | −£1.76 | −£0.48 | −£0.04 | −£3.48 |
| Position mark-to-market | −£1.09 | +£17.54 | +£26.71 | +£28.53 | −£99.86 |
Theta is what you are paid; delta decides the outcome. In the last column a single one-standard-deviation fall takes delta from +0.18 to +0.57, so the position stops behaving like a small income trade and starts behaving like 570 Tesco shares. That is where the trade changes character, and it happens well before the strike is breached.
UK worked example, in pounds
You would buy Tesco at 430p. It is trading at 454p.
Tesco (TSCO) traded around 454p on 17 August 2026. You sell 1× TSCO 430p put expiring Friday 18 September 2026, 32 days out. Assume the chain shows a 3.00p bid — twelve 0.25p ticks, consistent with implied volatility near 22% and a delta of about −0.18. This is an illustration, not a quote.
The comparison that matters. £28.60 on £4,300 is 0.665% over 32 days, about 7.6% annualised — and £1.40 of commission has already taken 4.7% of the gross premium. But the same £4,300 in an easy-access account at Bank Rate, held at 3.75% on 30 July 2026, earns roughly £14.14 over those 32 days for no risk. The put buys about £14.46 of extra return in exchange for £4,271.40 of downside. That is the honest arithmetic of writing puts on a low-volatility UK share, and why the IV-rank gate is not optional.
Base case — Tesco closes at 465p.
Adverse case — Tesco closes at 405p and you are assigned.
Favourable case — Tesco drifts to 462p and you take the profit rule.
This is a single, hand-picked, favourable scenario. It is not a typical or expected outcome. Most UK retail traders will do this on a US-listed name instead, where the contract is 100 shares, no SDRT arises, and every disposal — grant, buy-back, eventual share sale — must be converted into sterling at the spot rate on that date, so the sterling result can differ from the dollar result even when the dollar trade is flat. Add the broker's FX conversion spread to the cost line. Past performance, including any illustrative example, is not a reliable indicator of future results.
Management and adjustment
At this level you do not adjust. You close. Rolling a tested put is a Level 2 skill: it is two trades, it re-dates your tax point, and done badly it converts a small loss into a larger obligation for longer.
RULE — CLOSE, DO NOT ROLL. If the share breaches your strike and you no longer want the shares, buy the put back and take the loss. Do not roll down and out. Do not roll for a net debit under any circumstances: paying to stay in a losing credit trade adds risk to a position that has already told you it was wrong.
RULE — ACCEPT OR CLOSE, DECIDED IN ADVANCE. Write down before entry which regime you are in: "I want the shares at 430p", where there is no stop and assignment is a success, or "I want the premium", where the stop below applies and assignment is a failure. Traders lose money here by switching regime halfway through, after the price has moved.
RULE — EARLY ASSIGNMENT. ICE UK single-stock options are American style, so assignment can arrive on any business day, usually once the put is deep in the money and its remaining time value is negligible. If you are not willing to take delivery tomorrow morning, close today.
Exit rules
- Profit target: buy to close at 50% or less of the credit received — here 1.50p or less. Do not hold a nearly worthless option for the last few pounds.
- Stop: mechanical. Buy to close if the put trades at twice the credit — 6.00p. Realised loss £32.80, or 0.76% of the £4,300 collateral. Applies only in the "I want the premium" regime.
- Time stop: close at 21 days to expiry regardless of P&L — 28 August 2026 here. Gamma rises sharply in the last three weeks, which is when a manageable position becomes an unmanageable one.
- Assignment-avoidance exit: close before any ex-dividend date inside the window, and before 16:30 London on the third Friday, when the ICE series stops trading.
If all four are silent and expiry arrives, you take assignment and own the shares. That is the designed outcome, not an accident — which is why the underlying gate is the first row of the entry table.
Margin and broker reality
A cash account is sufficient: the collateral is the margin, and no borrowing is involved. You do need the broker's options permission, granted in the UK through trading permissions and an appropriateness assessment rather than the American "Level 1–4" ladder. Hargreaves Lansdown, AJ Bell and Trading 212 offer no options in any account, so this is an Interactive Brokers, Saxo or equivalent trade. The real cost is the ICE chain itself: on many UK names the quoted spread is a large fraction of the premium, and on a 3.00p option a half-penny of spread is a sixth of your income.
choose the underlying first, the strike second, the premium last. If you cannot name why the premium is fat, you are not being paid for the risk — you are the risk.What to trade instead
Simpler: a limit buy order plus a savings account. You forgo the premium but carry no obligation, no assignment date and no CGT event — and on a quiet FTSE 100 name the interest can be most of what the option would have paid. Use it whenever the IV gate fails.
More precise: the bull put spread, which buys a lower strike to cap the loss by construction rather than by collateral, freeing most of the £4,300 — at the cost of a smaller credit, a margin account and a Level 2 skill set. If you are assigned and keep the shares, the next step is the covered call; the two together are the Wheel, a system rather than a first trade.
First-trade checklist
Paper-trade gate: before real money, run three full 30–45 day cycles on paper, including one held deliberately into assignment, logging every leg with date, underlying, contract size, premium, costs and tax point.
- Confirm a GIA with options permission, and that the cash is idle.
- Name the share and the price you would pay in cash today. Write both down.
- Open the chain and read the contract specification — confirm the share count for that exact series.
- Check the calendar: no results, no ex-dividend date inside the expiry window.
- Pick the monthly expiry 30–45 days out, strike nearest −0.20 delta at or below your written price.
- Check bid-ask width and open interest against the entry table. If they fail, stop.
- Write down collateral, breakeven and maximum loss in pounds.
- Place a limit order at the mid. Never market-order a thin UK chain.
- Set alerts for 21 DTE and expiry Friday morning.
- Log the grant date. It is your tax point, and it is today.
Risk statement. Selling a put is taking on an obligation, and you can lose far more than the premium — up to £4,271.40 on this single contract, arriving all at once if the company fails. Options are complex instruments and are not suitable for everyone. This page explains how the instrument and its UK tax treatment work; it is not personal advice or a recommendation to trade. Figures are illustrative and were checked on 17 August 2026 — prices, premiums, fees and rates change.