Restrike sizes a monthly at-the-money short-put overlay against your actual account and tracks the whole cycle: contract count, margin cushion, expiry calendar. The discipline stops depending on you remembering.
Backtested across 8,424 overlapping cycles from 1993 to 2026, averaged across start days so that no single entry date sets the result. That span contains both 2008 and the 2020 crash, and the drawdown figures come from it rather than from a calm stretch. The growth figure is a rate rather than a dollar amount. On a hypothetical $100,000 portfolio it is the difference between 10.9% and 12.4% a year, before tax, and it does not get better on a larger account. Every figure on this page is hypothetical, describes past data, and is not a forecast or a promise of future results. Selling puts can lose far more than the premium collected.
It shows you the bad months too. In the same sample, 13% of cycles lost money and the worst lost 17.6 times what it collected. Sizing is most of what separates those two outcomes, which is the entire reason this tool exists.
Read straight down at any point. At 25% exposure the backtest turned 10.9% a year into 12.4%, and turned a −55.2% worst stretch into −58.0%. Selling more moves both, and the two panels are drawn to the same scale: one percentage point is the same height in each. The lower panel is taller because that movement really is about three times the size. The shaded band is the range that came through the worst month in the sample without being closed out; past it, the same fall closed the position at the bottom, which turns a drawdown you would have recovered from into a loss you keep. Backtested and hypothetical, as above.
How many contracts your account can actually carry at the level of exposure you pick, using the margin rules your broker really applies rather than a rule of thumb. Five contract types are covered, because one size does not fit every account: a single SPY contract is already too large for many six-figure portfolios, while SPYM is about an eighth of it and lets you land on a sensible number instead of rounding down to nothing.
See what the worst month on record does to your cushion before you are in it, not after. The shock test runs your position against a −32.8% fall and shows how far the market can move before your broker steps in, so you can pick a size you are comfortable holding through it.
Buy it back, re-strike at the money, resize. The expiry calendar tells you what is coming and the position log keeps an honest scorecard, with open positions kept separate because they are still real money and have not settled anything yet.
Selling a put means taking a premium now in exchange for an obligation to buy the index at a set price if it falls below that price before a set date. Most months nothing happens and you keep the premium. The overlay repeats that every month against a portfolio you already hold.
Sizing dominates everything else because the losses are rare and large rather than frequent and small. Across the sample, 13% of cycles lost money, and the worst single cycle lost 17.6 times what it collected. A position sized off the typical month is not sized for the month that matters.
Without an account, nothing leaves your browser. The calculator runs entirely on your device and there is no server to send anything to. The trade-off is that clearing your browsing data takes your position log with it, and it does not follow you to your phone.
Signing in changes exactly two things: your position log and your holdings are saved to your account, so they survive a cleared cache and appear on any device you sign in on. The figures you type into the calculator itself are still never sent. You can delete the synced copy at any time without deleting your account.
Exposure is the notional value of the puts you have sold: the number of contracts multiplied by the strike price and the contract size. It is what the position controls, not what it cost you. One put at a $600 strike on a 100-share contract is $60,000 of notional exposure, whatever premium you collected for it.
Every percentage on this page is that notional value as a share of your portfolio. At 25%, a $400,000 portfolio has sold $100,000 of notional. That is the number the sizing is built around, because it is what decides how much a fall actually costs you.
When you sell a put, your broker sets aside part of your account as collateral against the obligation you have taken on. That set-aside is the margin requirement, and it is what actually limits how many contracts you can sell, not the cash in your account.
Reg T is Regulation T, the US Federal Reserve rule that sets the minimum a broker must collect. It is the floor everyone starts from; no broker asks for less, and many ask for more. Restrike defaults to that floor and also carries Interactive Brokers’ published schedule, so you can see the difference. Whatever your own broker shows you is the number that counts. These are a deliberately conservative estimate.
Between 25% and 40% of notional is the range that survived the worst 30-day fall in the sample without being liquidated. Above roughly 40%, that same fall closes the position at the bottom, which turns a drawdown into a permanent loss.
An earlier version of this research put the range at 40–50%. That was published before the long-book margin correction and was optimistic: it assumed the shares you already hold demand no collateral of their own. They do, typically 25%.
Across the full 8,424-cycle sample, closing at 50% of maximum profit, the overlay retained roughly 28 cents per dollar of premium sold. Held to expiry across 402 non-overlapping windows the figure is higher, but those are different settings and the two numbers do not belong beside each other.
Neither number means anything without its drawdown, which is why −58% sits next to it above rather than in a footnote.
Restrike does arithmetic on numbers you type in and shows you what they imply. It does not recommend a position or forecast a return, and it will never place a trade or move money. That last line is the one that matters, and it does not move. Your broker’s margin figures are the ones that matter; these are an estimate, and a deliberately conservative one.
The calculator is free and stays free, on every device you sign in on. Pro is for the parts that only help if they happen without you remembering.
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