Does Theta Decay Over the Weekend?

Does theta decay over the weekend? Yes. The clock inside every standard option pricing model counts calendar days, and three calendar days pass between Friday's close and Monday's open. Where that decay lands is the part that surprises people: most of it comes out of Friday's quotes rather than Monday's, which leaves a Monday morning mark looking tamer than the three-day gap suggests.

Does theta decay over the weekend?

Theta is the rate at which an option's extrinsic value, the part of the premium above intrinsic value, shrinks as time passes. The models that produce it treat time to expiry as a calendar quantity. A contract expiring three weeks out carries 21 days of life in the formula, weekends included. Nothing in that math knows the exchange is dark on Saturday.

What turns the weekend into a step rather than a tick is the trading calendar. The panel below takes every SPY session in the twelve months to August 2026, groups them by weekday, and measures the calendar distance from each session to the next one.

WITH sessions AS
(
    SELECT date
    FROM global_markets.stocks_daily_aggs
    WHERE ticker = 'SPY'
      AND date >= '2025-08-01'
      AND date <  '2026-08-01'
    GROUP BY date
),
stepped AS
(
    SELECT
        toDayOfWeek(date) AS dow,
        dateDiff('day', date, leadInFrame(date) OVER (ORDER BY date ASC ROWS BETWEEN CURRENT ROW AND 1 FOLLOWING)) AS gap_days
    FROM sessions
)
SELECT
    ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'][dow] AS bucket,
    round(avg(gap_days), 2)                                       AS avg_days_to_next_session,
    max(gap_days)                                                 AS max_days_to_next_session
FROM stepped
WHERE gap_days BETWEEN 1 AND 10
GROUP BY dow
ORDER BY dow ASC

Monday through Thursday, a session hands off to the next after about 1 calendar day. Friday averages 3.08. The widest Friday step in the window measures 4 calendar days, which is a holiday Monday. Thursday has a long step of its own, reaching 4 calendar days: that is what a Friday holiday such as Good Friday or Juneteenth does to the session in front of it.

When is weekend decay priced in, Friday or Monday?

Quotes come out of a model whose time input runs to the expiration timestamp, not to the next open. Through Friday afternoon a market maker is already quoting a contract that will be three days older at the next chance to trade it, and the quoted premium walks toward that value across the session. By the close, much of the weekend already sits in the price.

Desks do not all weight the weekend identically. A common convention shrinks the volatility clock over hours the market is shut, on the observation that a closed market realizes almost no volatility. That leaves a weekend worth less than three ordinary days of decay and more than zero. The version that matters on a retail screen: Friday afternoon carries most of the step, and Monday's open carries the remainder alongside whatever the volatility level did in between.

One note on the number an account shows over the weekend. A Friday option closing mark is not a trade print. It is a quoted midpoint stamped at the close, and it is the value a statement carries until Monday's session reprices it.

How much premium does a weekend actually remove?

The size of a three-day step depends on how much time value is there to start with. For an at-the-money contract, model premium scales with roughly the square root of time to expiry: four times the time left is about twice the premium, not four times it. The curve is steep near expiry and nearly flat far out. Here is that shape in real closing prices, using SPY contracts struck within half a percent of the closing share price across the first half of 2026.

SELECT
    dte_bucket,
    round(avg(premium_pct), 3) AS avg_premium_pct
FROM
(
    SELECT
        multiIf(days_to_expiry <= 1,  '1 DTE',
                days_to_expiry <= 3,  '2-3 DTE',
                days_to_expiry <= 7,  '4-7 DTE',
                days_to_expiry <= 14, '8-14 DTE',
                days_to_expiry <= 30, '15-30 DTE',
                days_to_expiry <= 60, '31-60 DTE',
                                      '61-120 DTE')           AS dte_bucket,
        days_to_expiry                                        AS dte,
        100 * toFloat64(option_close) / toFloat64(underlying_close) AS premium_pct
    FROM global_markets.options_greeks
    WHERE underlying_symbol = 'SPY'
      AND date >= '2026-01-02'
      AND date <  '2026-07-01'
      AND iv_converged = 1
      AND volume > 0
      AND days_to_expiry BETWEEN 1 AND 120
      AND toFloat64(option_close) > 0
      AND abs(toFloat64(strike_price) / toFloat64(underlying_close) - 1) < 0.005
)
GROUP BY dte_bucket
ORDER BY min(dte) ASC

Contracts in the 1 DTE bucket closed at an average of 0.391% of the underlying share price. At the far end, the 61-120 DTE bucket averaged 3.199%. The multiple between those two figures is far smaller than the multiple in days left, which is the square root at work. The whole weekend question lives on that curve: three days out of sixty barely registers, while three days out of seven is about a quarter of the time value that remains.

Why does one day of theta under-predict Monday's mark?

The theta field on a platform is a derivative: the premium change implied by an instantaneous one-day step, with everything else held still. It is a rate, not a schedule, and the rate itself accelerates into expiry. Multiplying Friday's theta by three undercounts three days of calendar decay, and the shortfall grows as the contract shortens. The greeks change shape as expiry approaches, and theta's acceleration is the easiest of them to feel in a position.

The panel below runs that arithmetic on a real calendar. It takes a hypothetical at-the-money option expiring Friday, July 17, 2026, holds implied volatility fixed, and prints two figures for each SPY session in the month before: the share of premium a one-day step removes, and the share the actual step to the next session removes.

WITH sessions AS
(
    SELECT date
    FROM global_markets.stocks_daily_aggs
    WHERE ticker = 'SPY'
      AND date >= '2026-06-15'
      AND date <= '2026-07-14'
    GROUP BY date
),
stepped AS
(
    SELECT
        date,
        dateDiff('day', date, toDate('2026-07-17')) AS days_left,
        dateDiff('day', date, leadInFrame(date) OVER (ORDER BY date ASC ROWS BETWEEN CURRENT ROW AND 1 FOLLOWING)) AS step_days
    FROM sessions
)
SELECT
    toString(date)                   AS session_date,
    formatDateTime(date, '%a %b %e') AS session_label,
    step_days                        AS calendar_days_to_next_session,
    round(100 * (1 - sqrt(toFloat64(days_left - 1) / toFloat64(days_left))), 2)         AS one_day_pct,
    round(100 * (1 - sqrt(toFloat64(days_left - step_days) / toFloat64(days_left))), 2) AS actual_step_pct
FROM stepped
WHERE date <= '2026-07-10'
  AND step_days BETWEEN 1 AND 10
ORDER BY date ASC

On Mon Jun 15 the step to the next session is 1 calendar day, and the two columns agree at 1.57%. On the last Friday in the panel, Fri Jul 10, the one-day figure reads 7.42% while the actual step to Monday removes 24.41%. Every spike in the chart is a Friday, or a Thursday sitting in front of a market holiday, and the spikes grow toward the right as the square root curve steepens into expiry.

Those are model figures on a hypothetical contract with volatility pinned. No real option is promised to print them.

Is a Monday price change just weekend theta?

No. A Monday quote is a fresh price on a fresh volatility surface. Options are quoted in volatility as much as in dollars, and the volatility input does not hold still across a weekend. A Monday data release and ordinary supply and demand land in the same number the calendar step lands in.

SELECT
    ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'][dow] AS bucket,
    round(avg_iv * 100, 2)                                        AS avg_iv_pct,
    round((max(avg_iv) OVER () - min(avg_iv) OVER ()) * 100, 2)   AS weekday_spread_pts
FROM
(
    SELECT
        toDayOfWeek(date)       AS dow,
        avg(implied_volatility) AS avg_iv
    FROM global_markets.options_greeks
    WHERE underlying_symbol = 'SPY'
      AND date >= '2026-01-02'
      AND date <  '2026-07-01'
      AND iv_converged = 1
      AND volume > 0
      AND days_to_expiry BETWEEN 20 AND 45
      AND abs(toFloat64(strike_price) / toFloat64(underlying_close) - 1) < 0.05
      AND toDayOfWeek(date) <= 5
    GROUP BY dow
)
ORDER BY dow ASC

Across the first half of 2026, average implied volatility on near-the-money SPY contracts with 20 to 45 days to expiry spanned 0.22 volatility points from the lowest weekday average to the highest, with Monday at 16.93% and Friday at 16.96%. Those are averages over roughly twenty-five weeks, and a single weekend can move the level by more than that entire spread. When a Monday mark comes in under Friday's, the calendar step and the volatility change are both inside it, and the volatility number is what separates them.

FAQ

Does theta decay happen on Saturday and Sunday?

Time to expiry in a pricing model is calendar time, and Saturday and Sunday each remove a day of life from the contract. There are no quotes on those days, which is why the decay appears as a step between Friday's close and Monday's open rather than as a visible drip.

Is weekend theta priced in on Friday?

Much of it is. Market makers quote from a model whose clock runs to expiry, and by Friday's close the premium already sits close to what a three-day-older contract is worth. Many desks also discount weekend hours in the volatility clock, which leaves the weekend worth less than three ordinary days of decay and more than nothing.

Does a three-day holiday weekend decay more than a normal weekend?

In calendar terms, yes. A Friday close ahead of a holiday Monday sits four calendar days from the next session instead of three, and the first panel above shows a Thursday before a Friday holiday doing the same thing. The extra day counts for most on short-dated contracts, where each day is a large share of the time left.

Why does my platform's theta not match Monday's price change?

Theta is an instantaneous one-day rate quoted for the current moment. Three days of decay comes to more than three times that rate, as the rate accelerates into expiry, and Monday's price also carries any change in implied volatility and in the underlying. The theta field answers a narrower question than what the contract will be worth Monday.

Every panel here ships with the exact SQL beneath it. Open one and the arithmetic is auditable line by line. To draw the same decay curve on another underlying or another expiration date, ask for it in plain English on the Strasmore terminal.