Ad Inventory Sell-Through Rate: Formula and Calendar

Sell-through rate is the share of the ad inventory you offered for sale that actually got sold. The short answer: divide the units you have booked by the units you made available for the same period, then read the result as a percentage. The catch is that the answer depends entirely on what you count as a unit and what you leave out of the denominator. A site that sells a banner by the week and a site that sells impressions are running the same formula on two different things.

This guide is written for publishers who sell ads directly on their own sites, small media teams, and anyone running ad operations out of a spreadsheet. It sets up the formula and the denominator rules, separates forecast impressions from delivered ones, looks at seasonal gaps and holdbacks, explains how fill level should and should not influence price floors, and ends with a monthly inventory sheet you can copy. If you use an ad server such as Google Ad Manager the same logic applies; if you do not, a spreadsheet is enough. Nothing here is legal or financial advice, it is a planning method.

Sell-Through Formula and Denominator Pitfalls

The numerator is easy: booked units. The denominator is where most mistakes happen, because it should hold only the inventory that was genuinely for sale. Space you reserved for yourself, space that was switched off for a redesign, and space that has not launched yet are not sellable inventory, and counting them makes your rate look worse than your sales team deserves.

One formula, three ways to count

Pick the unit that matches how you sell. For fixed placements sold by time, the unit is a slot-week. For impression-based deals, it is a thousand impressions. For click or action based deals the unit is a predicted outcome, which is the least reliable base and best avoided for fill measurement.

• Slot-week count: booked slot-weeks divided by sellable slot-weeks. Three placements across a five-week month give fifteen sellable slot-weeks.
• Impression count: booked impressions divided by the impressions you expect to be sellable in that period.
• Revenue count: realized revenue divided by what the same inventory would have earned at list price if fully booked. This one captures discounting, but it also blends fill with pricing discipline, so treat it as a companion, not a replacement.

Track all three side by side for a few months. When the slot-week count is high and the revenue count is low, you are filling space, but with discounts. That gap is the starting point for a pricing conversation, not a reason to celebrate a high fill.

Pitfalls that distort the rate

Look closely at the first row. A banner promoting your own newsletter is not a sale. If it is in the numerator you will see strong fill without strong demand, and you will lose sight of how paid interest actually moves over the year.

A rule for choosing the base

Use this rule. If you sell fixed placements by time, measure fill in slot-weeks. If you guarantee impressions, measure in thousands of impressions. If you do both, keep two separate rates and do not merge them into one number, because a blended rate hides which sales channel needs work. For the pricing side of the story, read what drives ad space pricing.

Forecast vs Delivered Impressions

The moment you sell impressions, your denominator becomes a prediction. A forecast that misses the mark makes the fill rate misleading, so keep forecast and delivered in separate columns and compare them every period.

What the Ad Manager documentation says, and does not say

The Ad Manager Help page on future sell-through (Opens in a new tab) describes the future sell-through report as a report type that shows availability across your whole network and helps you decide whether there is room to book more line items. The page does not state a formula, and it does not define forecasted, available or reserved inventory. So the formulas above are working definitions used in practice, not wording taken from the page.

The page adds a few operational details. Creating the report does not run a simulation, it only counts rows that match the chosen dimensions and filters. Booked line item data is updated daily, which makes the report more likely to overestimate available inventory because of recent activity. The look-ahead is limited to 90 days at daily granularity and one year at monthly granularity, and the underlying simulation data covers an 18-month period. Read together, these facts tell you how much weight a forecast can carry: a sale made this morning may not show up yet, and a month far in the future is a rough guide, not a promise.

The same page marks the feature as deprecated. According to Google's page, the Reports tool was scheduled to be deactivated in the third quarter of 2026; check whether the interface still exists in your account. Publishers are directed to Interactive reports, which are available to all Ad Manager publishers, and no specific removal date is given. If you use Ad Manager, look in your own interface to see whether the report is still there. If it is not, monitor availability through interactive reports and your own sheet. Product names change; the discipline of separating forecast from delivery does not.

Measuring forecast drift

Add a drift column: delivered impressions divided by forecast impressions. One month of drift tells you little. Three periods drifting the same way tells you your method is biased.

1. Record the forecast at the time of sale and date it.
2. After the period closes, write delivered impressions on the same row.
3. Compute drift and add a one-line cause: traffic dip, template change, unusually heavy campaign, or ad-serving loss.
4. If drift points the same way for three periods, adjust future forecasts by that margin.
5. Apply the adjusted forecast only to new sales, never to contracts already running.

Example scenario: a tech review site forecasts weekly impressions for its top leaderboard. A product launch week produces far more traffic than predicted, and the two weeks after are quiet. Flag the launch week as an outlier in the drift column and keep it out of the average, otherwise one event bends your whole method.

Guaranteed deals and leftover fills

Impressions you guaranteed to an advertiser are reserved up front and belong in the booked numerator. Unguaranteed deals, house ads and remnant fills use inventory that would have gone empty, but they do not prove demand. Put them on separate rows so that direct-sold fill and total utilization are two different figures. If you merge them, a high utilization number can make a weak direct sales quarter look healthy.

Seasonality and Holdbacks

Fill is not flat across the year. Some months are crowded with advertisers and others are quiet because budgets shrink. Planning on a yearly average sells peak weeks too cheaply and leaves the troughs empty.

Holdbacks and the calendar layers

A booking calendar needs four layers. Confirmed bookings are signed and paid. Options are placements held for a named advertiser until a deadline. Holdbacks are periods you keep for renewals, for your own campaigns or as a buffer for makegoods. Closed periods are placements switched off for maintenance or redesign.

The reason to keep options out of the main rate is simple. If a held slot counts as sold, your rate drops sharply the day the option expires and you may read that as a demand drop. Tracking confirmed and optioned fill separately shows you real fill and likely fill at the same time. For a campaign-side view of the calendar, see seasonal campaign booking and calendar.

Booking lead time

Advertisers planning seasonal pushes look for space weeks ahead. Define your furthest bookable date and track fill for fixed horizons: thirty days out, sixty days out. Forward fill and current fill are different measurements. Current fill reflects sales made in the past; forward fill reflects how your sales effort is doing today.

The ninety-day look-ahead in the Ad Manager page is a useful reminder that forecasts get weaker with distance. You can keep a longer horizon in your sheet, but read far-off months with extra caution.

What to do with gaps as they approach

If a week is still open as it gets close, work through a fixed order. First send a short offer to past advertisers. Second, offer a short renewable package. Third, consider using the space for your own content rather than discounting it. A last-minute discount rescues fill in the short term but teaches buyers that waiting is cheaper. Write the discount rule down in advance: how many days out, how much off, and for which package.

Tracking how options turn into bookings

Record how many options you opened in a period, how many were confirmed, and how many expired. The ratio shows whether your quote, your price or the option window is the problem. A very long option window blocks space for no reason; a very short one lets the slot free up before a buyer can get budget approval. Base the window on how long past options actually took to resolve rather than on a fixed number of days.

Give each option record an advertiser name, the held placement and dates, an expiry day, the package quoted and a note if a second buyer is interested. With that note you can queue the second buyer instead of guessing, and nobody is promised priority they were not given.

Price Floors by Fill Level

Fill is a signal for pricing, not an instruction. High fill may mean the price is too low; low fill may mean the price or package does not match demand. But low fill can also come from a weak placement or from falling traffic, which no discount will repair.

A first reading of fill against price

None of these rows is an automatic price change. Each is a reason to run a test, and a test only teaches you something if you change one variable at a time: price, package length or placement.

Writing a simple floor rule

If you want to adjust floors by fill level, write the rule before the quarter begins. For instance, once a period reaches a stated fill level ahead of its start date, the list price rises; if it does not, a shorter package is offered. Take the thresholds from your own history. Numbers borrowed from another site reflect that site's traffic and buyers, not yours.

For a broader view of how rates are formed, see what drives ad space pricing, and for the whole direct-sales process see selling ad space on your own website. Both help you connect the fill figure in this guide to an actual price decision.

Retention and fill

A good part of your fill comes from advertisers who buy again. When retention is strong you do not need to find new buyers every month to keep fill steady. Measure it separately: of the advertisers whose campaign ended, how many rebooked the same placement. How to read that number is covered in renewal decision and end-of-campaign review.

Segmenting by placement and template

Total fill can look healthy while individual placements tell different stories. A top banner on a guide page and a footer banner on archive pages are not the same product. Break the data out by position, by page template and by sales type. Seeing each separately shows which placements are strong products and which need rework.

If you bundle a weak placement with a strong one, track the bundle on its own row so you can see whether the discount actually fills the weak slot. The bundled slots should still count by placement, otherwise the strong placement's fill hides the weak one.

A Simple Monthly Inventory Sheet

The layout below is a column structure you can paste into a spreadsheet. Each placement is a row and each month is a block. Even with a handful of rows the rate comes out correctly.

The two most valuable columns are sellable units and likely fill rate. The first prevents denominator errors and the second prevents the option illusion. At the end of each month, copy the block and start a new one. Do not overwrite the old month, or you lose the curve over time.

A monthly review checklist

• Does sellable units exclude holdbacks and closed periods?
• Are options counted separately with an expiry date?
• Are guaranteed and remnant sales on different rows?
• Has drift gone the same way for three periods?
• How far below list price is the average realized price, and do your discount rules explain it?
• Have you calculated likely fill for the next thirty and sixty days?
• Which advertisers are waiting on a renewal decision?
• Was any unusual week or campaign annotated?

A worked reading

Example scenario: a newsletter publisher sells a top sponsor slot and a mid-issue slot. The top slot books early every month and its realized price stays close to list. The mid-issue slot is often empty and, when it does sell, it sells at a discount. The sheet shows two different problems. For the top slot, a small increase is worth testing. For the mid-issue slot, check where it sits in the issue and what reporting buyers get before touching price. One blended fill rate would have averaged the two stories into nothing.

Common misunderstandings

• "Full fill is the goal." Constant sell-outs can mean prices are low or that new buyers have nowhere to go. Read fill together with revenue and retention.
• "Low fill means discount more." Find the cause first: demand, placement, package or measurement.
• "One rate is enough." Keep rates by placement, template and sale type, then add a total.
• "If the forecast is off, the rate is useless." Track drift separately and fill stays useful.

Frequently Asked Questions

What is sell-through rate and how do I calculate it?

Sell-through rate is the share of sellable ad inventory that has been sold. Divide booked units by sellable units for the same period. The unit can be a slot-week or a thousand impressions. The Ad Manager Help page gives no formula for its report, so write down the definition you use.

What is a good sell-through rate?

There is no universal threshold and another site's figure does not reflect your demand. Compare against your own past periods, by placement and with the same unit type. Constantly high fill can mean prices are low, and constantly low fill can point to a placement, audience or package mismatch.

Should an optioned slot count as sold?

No. Keep confirmed bookings and options separate. If options count as sold, the rate drops sharply when they expire and looks like a demand collapse. Track confirmed fill and likely fill, which includes options, in two columns.

Can I still use the Ad Manager future sell-through report?

The Ad Manager Help page marks the report as deprecated. According to Google's page, the Reports tool was scheduled to be deactivated in the third quarter of 2026; check whether the interface still exists in your account. No specific date is given. If it is gone, use interactive reports and your own sheet.

Is discounting the right way to fill open slots?

Sometimes, but set the rule in advance. Random last-minute discounts teach buyers to wait. A more defensible order is an offer to past advertisers, then a short package, and only then a discount or using the space for your own content.

Why separate guaranteed sales from remnant fills?

Remnant and unguaranteed fills use space that would have stayed empty and do not prove new demand. Mixed into one rate, they make direct sales look stronger than they are. Separate rows show which channel is actually growing.

How often should I update the sheet?

Weekly if you sell frequently, otherwise monthly. Open a new block each month and leave old months untouched so you can analyse drift and seasonality over time.

Conclusion

Sell-through is useful when the denominator is honest. Count only inventory that was truly for sale, keep confirmed bookings apart from options, compare forecast with delivered impressions, separate guaranteed deals from remnant fills, and never treat fill as the only reason to change a price. The Ad Manager Help page gives no formula for its future sell-through report and marks the feature as deprecated, so owning your definitions and keeping a tool-independent sheet is the safest route. This article offers a method only and is not legal or financial advice.

If you want to offer your own inventory for direct sale, you can look at the ad spaces page at Akua Adforce; scope and terms are on that product page.