The number a pacing guide is missing
Curriculum documents are written in lessons. Timetables are written in periods. The two are treated as the same unit, and they are not, because a lesson is a quantity of content and a period is a slot that may or may not happen. A unit described as fourteen lessons in a five week window with four periods a week looks like it has six periods to spare. Subtract three closure periods, two interrupted periods and three periods of assessment and the twenty scheduled periods have become twelve of teaching. Fourteen lessons into twelve periods does not go, and no amount of planning at the start of the unit reveals that, because at the start of the unit the interruptions have not been announced yet.
This is the whole purpose of the calculation. It does not produce a schedule. A schedule would be a lie, because you do not know which Tuesday the fire drill lands on. It produces the gap, which is knowable in advance from historical averages, and it produces it in the units the decision gets made in — how many lessons have to come out.
Counting the losses honestly
The most common error is counting calendar days off rather than periods of this class lost. A school closed on Monday and Tuesday costs a class that meets daily two periods, and costs a class that meets Tuesday and Thursday only one. Count in periods of the specific class.
| Category | What belongs in it |
|---|---|
| Closures and holidays | Scheduled days off, weather closures, professional development days, anything on the published calendar |
| Interruptions | Assemblies, drills, picture and yearbook time, testing windows that pull students out, field trips, half days, late starts, your own absences whether or not a substitute covered |
| Assessment and review | The unit test, quizzes, the review period before, the period spent handing back and going over |
Assessment sits in its own row rather than under losses because it is not lost time — it is time spent on something other than new content. Keeping it separate means the arithmetic reports two useful figures rather than one: how many periods actually meet, and how many of those carry new material.
The slippage allowance
Set it to zero and the calculation assumes every lesson finishes inside its period. Some do. The ones that do not are usually the ones the unit depends on, because a lesson runs long when the class did not follow it, which is exactly when moving on is worst. Ten percent on a fourteen lesson unit is one and a half extra periods, which is roughly one lesson repeated and one running twenty minutes over. Fifteen percent is a more honest figure for a new unit, for a class you have taught for less than a term, or for material with a hard prerequisite in it.
There is no right value and this page does not suggest one as a standard. It is worth deriving your own from the last unit: count the lessons you planned and the periods you spent, divide, and use that.
What to do with a shortfall
The three closures the tool prints are the only three that exist, and they are not equally good. Cutting lessons is a curriculum decision that belongs with a department rather than with a spreadsheet, and which lessons can go is not a question arithmetic can touch. Adding periods usually means taking them from the next unit, which moves the problem rather than solving it, though moving a problem into a term with fewer interruptions in it is sometimes a real fix. Compressing every lesson is the option that happens by default when nobody decides anything, and it is the one worth naming explicitly, because the tool will tell you what percentage of each planned lesson actually fits and the figure is often uncomfortable enough to force a real choice.
The fourth option, which the calculation deliberately does not offer, is discovering the gap in week four and absorbing it into the last two lessons of the unit. That is what happens when nobody runs the numbers, and it lands the compression on whatever the unit ends with, which is usually the hardest material and the part with the least review time behind it.
Alongside this: the timetable maker builds a printable weekly grid once the pattern is settled, the study plan calculator does the same arithmetic from the revision side for material measured in pages, and the business day calculator counts working days between two dates when you need the calendar side rather than the period count. If assessment periods are eating the plan, the quiz sheet maker is on the site too.
Questions people ask
How many periods should I assume are lost in a term?
This page will not put a number on it, because it varies by school, by term and by grade level more than any single figure could survive. What it will do is give you a way to find your own: take last year of the same term, count the periods this class was scheduled to meet, count the ones that actually met, and use the difference. Most teachers who do this once are surprised on the high side, and the terms with standardised testing windows in them are usually the worst. The sensitivity table in the results shows what a few more lost periods do, which is often more useful than a precise starting estimate.
Should assessment periods count as teaching periods?
That depends on what your unit plan already includes, and getting it wrong double counts. If the fourteen lessons in your unit already have the test and the review day inside them, set the assessment field to zero, or you will be subtracting the same periods twice. If the fourteen are fourteen periods of new content with the test on top, put the assessment periods in the field. The tool cannot tell which convention your pacing document uses, and the two produce answers that differ by several periods on a typical unit.
What if the class meets on a rotating or block schedule?
Work in periods rather than days and it handles itself. A block schedule where the class meets three times one week and two the next averages two and a half periods a week, so enter 2.5 and put the actual period length in the minutes field. The output is then in blocks rather than in traditional periods, which is what you want, since a lesson written for a fifty minute period is not one block of content. If your unit was written for short periods and you teach it in blocks, the lesson count needs converting before it goes in the top field, and that conversion is not a clean multiplication.
Why does it not produce a day-by-day schedule?
Because the schedule would be the least reliable thing on the page. The losses that break pacing are not known in advance — you do not know which week the drill lands in, or which lesson the class will need twice. A calendar that lays fourteen lessons onto fourteen named dates looks authoritative and is wrong by the second week, and once it is wrong it stops being consulted. The gap between what you have and what the unit needs is knowable at the planning stage from averages, it is the number the decision actually turns on, and it stays true regardless of which Tuesday the assembly falls on.
The result says the unit runs past the deadline. Now what?
The tool shows three closures and none of them is free. Cutting lessons is a curriculum judgement about what can go, which is a department conversation rather than an arithmetic one. Adding periods borrows from the next unit and needs to be checked against that unit having the same problem. Compressing everything is what happens by default, and the results print the percentage of each planned lesson that actually fits so the size of the compression is visible rather than implicit. The value of running this before the unit starts is that all three are still available in week one and only the third is still available in week four.