If you have ever studied fixed-time and fixed-interval schedules, understood them, moved on—and then had to look them up again two weeks later, you are not alone.
They are easy to confuse because both contain the word fixed, both involve time, and both can involve delivery of the same reinforcer. But there is one question that separates them:
Does a response have to occur for the reinforcer to be delivered?
If you can answer that, FT versus FI becomes much easier.
Here is the distinction worth remembering:
That second arrow is where the distinction lives. Under a fixed-interval schedule, the passage of time does not produce reinforcement by itself — the interval has to elapse, and then a response is required. Under a fixed-time schedule, no response is required for the programmed delivery.
| Schedule | Time matters? | Response criterion? | What produces delivery? |
|---|---|---|---|
| FT | Yes | No | Elapsed time |
| FI | Yes | Yes — a response after the interval | First qualifying response after the interval |
| FR | Not as the requirement | Yes — response count | Fixed number of responses |
| DRO | Yes | Yes — target response must remain absent | Meeting the no-target-behavior criterion |
One of the easiest mistakes is to see "five minutes" and immediately think fixed interval. Don't classify the schedule from the presence of time alone — ask what happens after the time passes.
Suppose a client receives 30 seconds of attention every five minutes regardless of what they are doing. Five minutes pass. Attention is delivered. The client does not have to request attention, complete a task, or refrain from problem behavior for the entire five minutes. The programmed delivery occurs because the scheduled amount of time elapsed.
Five minutes pass → reinforcer delivered.
There is no response requirement for the scheduled delivery. That is why FT schedules are described as response-independent.
Now imagine a different arrangement. A learner can earn attention on an FI 5-minute schedule. Five minutes pass. Nothing necessarily happens yet. The first qualifying response after those five minutes produces the reinforcer.
Five minutes pass → reinforcement becomes available → next qualifying response produces reinforcement.
Responding during the interval does not satisfy the schedule early. Once the fixed interval has elapsed, the next qualifying response contacts reinforcement — which is also why describing fixed interval as noncontingent reinforcement is technically incorrect. There is still a contingency. A response is required.
This may be the easiest exam-day discrimination. Imagine the person makes zero responses.
If the learner does absolutely nothing, will the programmed delivery still occur?
If yes, FT is possible. If no — because a response must occur after the interval — think FI.
This is where the terminology gets a little more nuanced. Fixed-time and NCR are closely related, but they are not best treated as interchangeable terms.
In applied behavior analysis, noncontingent reinforcement (NCR) is the commonly used term for an intervention in which stimuli with known or presumed reinforcing effects are delivered independently of the target response. Fixed-time and variable-time schedules are common ways to arrange those response-independent deliveries.
NCR describes the applied intervention arrangement. FT describes a fixed temporal schedule for arranging response-independent deliveries.
For example: attention delivered every five minutes independently of problem behavior is NCR on FT 5 min. Attention delivered at varying intervals averaging five minutes, again independently of problem behavior, is NCR on VT 5 min. Both arrangements are response-independent. Only the first uses a fixed-time schedule.
DRO creates another common trap because it also uses time. Consider three examples, all built around the same five minutes and the same reinforcer.
Nothing the learner does determines whether the scheduled five-minute delivery occurs.
Time must pass and then a response must occur.
Time matters, but reinforcement is contingent on the absence of the target behavior.
FT: time only. FI: time + response. DRO: time + omission criterion.
Do not let "five minutes" choose the answer for you.
In everyday language, contingent can sound like "planned," "conditional," or "scheduled." That is not the important distinction here. In behavior analysis, the relevant question is whether delivery depends on a specified relation to behavior.
Under FI, it does — the response after the interval matters. Under DRO, it does — the absence of the target behavior during the specified period matters. Under FT, it does not. The clock alone determines the programmed delivery.
Try each before reading the answer column.
| Scenario | Schedule | Why |
|---|---|---|
| An office coffee machine dispenses a free cup every 30 minutes whether anyone presses a button or not. | FT 30 min | Elapsed time alone produces the scheduled delivery. |
| A student can earn a token for the first completed math problem after ten minutes have elapsed. | FI 10 min | Ten minutes must pass, but completion of a problem is still required. |
| A learner receives a two-minute break after completing every five tasks. | FR 5 | The controlling requirement is response count, not elapsed time. |
| A teacher provides attention whenever five minutes pass with no calling out. | DRO 5 min | The reinforcer depends on omission of the target behavior for the specified period. |
Suppose attention is the reinforcer in every option. That tells you almost nothing about the schedule. The schedule is defined by the relation between responding, time, and reinforcement — not by what the reinforcer happens to be.
| Stem | Schedule |
|---|---|
| Attention every 10 minutes regardless of behavior. | FT |
| Attention following the first request after 10 minutes. | FI |
| Attention after 10 minutes with no aggression. | DRO |
| Attention after every 10 requests. | FR 10 |
Same reinforcer. Completely different contingencies.
Watch how much one phrase can hide: "Reinforcement is delivered after five minutes." That statement is incomplete. You still need to know — after five minutes, what?
The time value alone does not identify the schedule.
Instead of memorizing isolated definitions, practice identifying the requirement for reinforcement. When you read a schedule question, mentally complete this sentence: "The reinforcer is delivered when __________."
That approach is more durable than matching vocabulary words.
You may see fixed-time described casually as a "reinforcement schedule," especially in applied discussions of NCR. The important functional distinction is that FT is a response-independent schedule of programmed stimulus or reinforcer delivery. Unlike FI, the scheduled event is not delivered contingent on a particular response.
For exam reasoning, that distinction matters more than getting stuck on terminology. The useful question remains: what does the organism have to do for the scheduled event to occur? For FT, the answer is nothing. For FI, the answer is respond after the interval has elapsed.
Before reading the breakdown, work this one the way you would on exam day.
A behavior technician is instructed to provide a preferred item on a 5-minute fixed-time schedule. The technician starts a timer after each delivery. When the timer reaches 5 minutes, however, the technician waits until the learner next makes an appropriate request before providing the item and restarting the timer. Which schedule is the technician actually implementing?
The technician may have intended to implement FT 5 minutes, but the actual contingency is different. After five minutes pass, the preferred item is not delivered automatically — the learner must make an appropriate request first. That means the interval determines when reinforcement becomes available, and the first qualifying response after the interval produces it. Under a true FT schedule, the programmed delivery would occur after five minutes regardless of whether the learner requested, stayed silent, or made no response at all. DRO is also wrong, since reinforcement isn't contingent on the absence of a target response throughout the interval. And although one request occurs before each delivery, it isn't simply FR 1 — that request can't produce reinforcement until the five-minute interval has first elapsed. Classify the schedule by the contingency that is actually operating, not by the schedule the implementer intended to use.
You do not need four paragraphs in your head during the exam. You need this:
FT = the clock delivers it. FI = the clock makes it available; the next response earns it.
And if you are still unsure, ask: what happens if no response ever occurs? Under FT, the scheduled delivery still happens. Under FI, it doesn't. Once that difference becomes fluent, two schedules that used to look almost identical become very difficult to confuse.
| Stem | Schedule |
|---|---|
| A client receives access to music every 15 minutes regardless of behavior. | FT |
| After 15 minutes have passed, the client's next completed work response produces music. | FI |
| The client receives music after 15 minutes without yelling. | DRO |
| The client receives music after every 15 completed work responses. | FR 15 |
Don't classify the schedule by the number or the clock. Classify it by what behavior — if any — is required for reinforcement.
Knowing the definitions is only the starting point. BA Prep tests whether you can hold FT, FI, FR, and DRO apart when the examples share the same reinforcer and the same number of minutes — the kind of schedule discrimination required by the BCBA 6th Edition Test Content Outline.
Start Free TrialBehavior Analyst Certification Board. (2022). BCBA test content outline (6th ed.). Behavior Analyst Certification Board. Updated September 2024. See B.9 for simple schedules of reinforcement and G.3 for time-based reinforcement procedures. https://www.bacb.com/wp-content/bcba-outline-6thEd/
Vollmer, T. R., Iwata, B. A., Zarcone, J. R., Smith, R. G., & Mazaleski, J. L. (1993). The role of attention in the treatment of attention-maintained self-injurious behavior: Noncontingent reinforcement and differential reinforcement of other behavior. Journal of Applied Behavior Analysis, 26(1), 9–21. https://doi.org/10.1901/jaba.1993.26-9
Poling, A., & Normand, M. P. (1999). Noncontingent reinforcement: An inappropriate description of time-based schedules that reduce behavior. Journal of Applied Behavior Analysis, 32(2), 237–238. https://doi.org/10.1901/jaba.1999.32-237
Borrero, J. C., Bartels-Meints, J. A., Sy, J. R., & Francisco, M. T. (2011). Fixed-time schedule effects in combination with response-dependent schedules. Journal of Applied Behavior Analysis, 44(1), 163–167. https://doi.org/10.1901/jaba.2011.44-163