The expiry is the day an option dies: after that day, it is worth nothing. The same SPX 7500 call might cost $2.00 of premium expiring today, but $20.00 expiring a month out — the extra money isn't buying a different option, it's buying time. Picking an expiry is really picking a speed: do you want SPX to move within hours, or give it weeks to get there? This page works out the math for all three first, then shows how to practice it in the simulator.
How the three expiries differ
A 0DTE expires today: the premium is the cheapest, because only a few hours of time value are left; a 1% SPX move is about 75 points in a day, so if the direction is right you win fast — if it's wrong, or SPX doesn't move, the premium is zero by the close.
A weekly expires in a few days: the premium costs more than a 0DTE and less than a monthly; the extra days are room for error — if SPX doesn't move today, tomorrow is still a chance — but every extra day is paid for in time value.
A monthly expires in a few weeks: the premium is the most expensive, because it holds the most time; SPX has weeks to move your way — and weeks to move against you. If the direction is right you don't have to cash in right away; if it's wrong, the loss is sized on the bigger number too.
The numbers below are examples, not real quotes: say SPX is at 7550 and the same 7500 call costs $2.00 expiring today, $8.00 expiring in a week, and $20.00 expiring in a month; buying 1 contract costs $200, $800, or $2,000 in premium — ten times more, and all you're buying is time.
Time value decays at different speeds
Time value only exists before expiry: a 0DTE has only today left, so its time value drains the fastest — an option that looks fine in the morning can be nearly worthless by the afternoon. The buyer pays for time; the seller collects for it.
A weekly decays day by day: with a few days left, each day drains much slower than a 0DTE; in the final day or two, the drain catches up with a 0DTE — a weekly isn't a slow 0DTE, its last day or two IS a 0DTE.
A monthly decays the slowest: in the first few days after opening, the time value barely seems to move; the closer to expiry, the faster it drains — time decay isn't steady, it speeds up toward the end.
So the shorter the expiry, the more the trade tests your timing: a 0DTE needs the direction today, a weekly lets you wait a few days, a monthly lets you wait a few weeks. Ask "how soon will the direction show up" first, then pick the expiry — not the other way round.
How to practice in the simulator
First, the plain truth: the simulator shows one expiry chain at a time, normally today (0DTE); on weekends or after the close, when there is no chain for today, it shows the next trading day's expiry and clearly labels it as not a 0DTE — check which day today's chain expires before you practice.
How to practice: build a feel with 0DTE first — say you buy 1 contract of the 7500 call for $2.00 of premium, the breakeven is 7500 + 2.00 + 0.013 = 7502.01; SPX has to settle above 7502.01 for a profit. If SPX doesn't move or falls, the most you lose is the $200 of premium plus $1.30 of round-trip fees, $201.30 in total.
The same math works for weekly and monthly, just with bigger numbers: say the same call expiring in a week costs $8.00 of premium, the breakeven is 7508.01 and the most you lose is $801.30; expiring in a month at $20.00 of premium, the breakeven is 7520.01 and the most you lose is $2,001.30 — the more time you buy, the further SPX has to travel, and the bigger the loss can be.
The discipline stays the same: $0.65 per contract per side in fees, at most 3 opens a day, a $60 fee breaker, and no new opens after 3:30 p.m. ET; write your exit plan before you submit, and don't leave it to the close.
Four mistakes beginners make
Buying a 0DTE just because the premium looks cheap: a $2.00 option looks cheap, but SPX has to rise past 7502.01 for a profit — if it doesn't move, the whole $201.30 is gone. What's cheap isn't the cost, it's how little time SPX gets to move.
Thinking a longer expiry is safer: a monthly option costs $20.00 of premium, so 1 contract can lose up to $2,001.30 — about 10 times the 0DTE. The more time you buy, the bigger the loss can be; don't only look at "no rush to expire".
Treating a weekly like a 0DTE and leaving it to the close: in its final day, a weekly drains just as fast as a 0DTE — having days left doesn't mean you can hold it forever; handle the last day or two on a 0DTE rhythm.
Forgetting that holidays and half-day sessions change the expiry: the expiry can come earlier before a holiday, and the close comes earlier on a half day — the chain on the page shows the real expiry, so check which day it is before you work out the breakeven.
This simulator uses real CBOE option chains delayed about 15 minutes, starts with $10,000 in virtual funds, charges $0.65 per contract per side in fees, and shows P&L net of fees; short-sale margin is a simplified simulated rule at 20% of the strike, not a real broker margin. The simulator is for practicing orders, discipline, and review. It is not investment advice and promises no returns.