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@pboongird conceptually it is even simpler: for the implied volatility you take a theoretical value with a constant time to maturity of 30 days (similar like the VIX). That makes values comparable. You intrapolate it I think from the four existing most ATM and most around 30 days TTM which are actually traded. So the maturities constantly keep changing over time. For the range you simply look at the time from one year back until yesterday.

I would like to write about my impression of Tradier after using them for a couple of weeks. 0. The promo $40/mo flat fee is great. It allows to be 1 cent per spread with 2 legs more agressive and still 'outperform' those who place trades in IB. 1. They do care and reply emails very fast. I asked all sorts of questions about transfers, reimbursement of wire transfers, why bid-ask is different from IB, etc. Personal attention, very good feeling regarding their support. 2. The tools they list at https://brokerage.tradier.com/platforms are either expensive to try or just suck for options. I tried several. The notable exception is ONE (option net explorer, Kim posted a discount to that tool somewhere in forums.). ONE integrates well with Tradier, but I need to adjust the fill prices in ONE after the order is filled if the price changed after playing with the order in Tradier. But there is a way to push the trade to Tradier from ONE without 'commit', which allows to wait and enter the real price, and do it only once. (ONE's support is also awesome, by the way. They are working on a tighter integration, they told me. Judging by their progress so far, it might happen in a couple of years... They are a small company.) One nice thing about ONE-Tradier compared to ONE-IB integration is that you do not need to keep the 2nd client open besides ONE. The Tradier's api is much more contemporary and does not require any client like IB demands. 3. Tradier's own web site is decent. Even on the go, in a horizontal layout on a larger phone, it is possible to enter spread orders, and it is MUCH more straightforward process than, for example, in IB TWS Mobile app. Monitoring open positions on Tradier's web site is hard, they do not combine legs into spreads in that particular view. If you are a programmer, their API is nice and clean. I wrote a python script that combines legs for me. Monitoring the open positions in ONE is a pleasure, unless they go south, of course. 4. Liquidity (part 1). There is no statistical significance yet in my observations. The first reason for that is that I did not place enough trades with them to be able to make conclusions. The second reason is that I was unaware of the different way IB presents bid/ask values from how it is done in Tradier, and that confused me for a while. Judging by few trades, I would say that fills in IB are faster. However, since the promo 40/mo flat allows to be more agressive, I will experiment with that more. No real conclusions yet. 5. Liquidity (part 2). The first 2 snapshots below are for the same trade in ToS Mobile (vertical) and Tradier. I see that the numbers are the same, including the size values. If those numbers would directly translate to fills, then one might expect similar fills in Tradier and ToS. The last 2 snapshots below are for the same trade in IB and Tradier. The bid-ask numbers for individual legs are the same, BUT the bid-ask values for the whole spread are calculated differently in IB. I do not know how they come up with those numbers in IB (weighted average?), but of course it is much easier to enter the position at IB's calculated mid! I was not aware of that for a while and thought the liquidity of something is not right in Tradier, until I started placing trades side by side. Besides that, the sizes are slightly better in IB (check the last 2 pics), which probably should translate to some added liquidity. (Tradier routes their orders through Citadel Securities and Knight Securities, if you are interested.) Overall, for the unsuspecting traders like myself, IB's way of calculating whole spread bid-asks (and mids) makes an impression that it is easier to fill orders in IB, because their mids are higher than in ToS and Tradier, and (can you imagine) it is easier to get the fill for the higher price. ------- I will try to place some more trades side by side and report back. So far, I like Tradier a lot. I hope their business model, open API etc will keep them competitive.