Best Spaced Repetition Intervals for Maximum Retention

You've heard spaced repetition works. But the magic isn't in the concept—it's in the timing. Get the intervals wrong, and you're either cramming too often (wasting time) or reviewing too late (watching your hard work evaporate). Get them right, and you can boost long-term retention by up to 50% compared to massed practice, according to a landmark study by Cepeda et al. (2006).

This guide breaks down the best spaced repetition intervals for every type of learner—whether you're grinding through medical boards, mastering a new language, or leveling up your coding skills. We'll cover the science, the schedules, and how to customize them in your favorite SRS app.

What Is the Forgetting Curve and Why Do Intervals Matter?

The forgetting curve, first described by Hermann Ebbinghaus in 1885, shows that we forget information exponentially fast unless we actively recall it. Within 24 hours of learning something new, you'll forget about 50-80% of it. Spaced repetition intervals are designed to interrupt this decay at the perfect moment—just before you'd forget—so each review strengthens the memory trace.

The key insight from Pashler et al. (2007) is that the optimal review interval is approximately 10-20% of the time until the next forgetting event. In plain English: if you'd forget a fact in 10 days, review it after 1-2 days. This "just-in-time" approach is what separates effective spaced repetition from random cramming.

Learn more about the science behind spaced repetition before diving into the intervals.

What Are the Best Spaced Repetition Intervals for Language Learning?

For vocabulary, grammar rules, and phrases, a common starting schedule is: 1 day → 3 days → 7 days → 14 days → 1 month → 2 months. This schedule works well because language learning involves thousands of small, discrete facts (words) that benefit from frequent initial reviews.

Adjust based on your recall success rate. If you consistently mark cards as "easy," stretch the intervals by 1.5x or 2x. If you're struggling, shorten the initial steps. The goal is to find the sweet spot where you're challenged but not overwhelmed.

Read our full guide on spaced repetition for language learning for more specific strategies.

How Do I Customize Intervals in Anki?

Anki gives you granular control over intervals. To customize them, go to the deck options and adjust the following settings under the "Reviews" tab:

• Steps (in minutes): The initial learning steps (e.g., 1 10) — these are your first two reviews within the same session.
• Graduating interval: The interval after you pass the learning steps (default: 1 day).
• Easy interval: The interval when you mark a card as "easy" (default: 4 days).
• Maximum interval: The longest interval before a card is considered "mature" (default: 365 days).

For most users, the default Anki settings are a good starting point. But if you want to optimize further, consider using the FSRS (Free Spaced Repetition Scheduler) algorithm, which adapts intervals based on your personal recall history. Learn more about SRS algorithms here.

Should I Use the Same Intervals for All Subjects?

No. The type of material dramatically affects the optimal interval. Here's a quick guide:

• Factual material (dates, definitions, drug names): Shorter initial intervals (e.g., 1-3-7 days) because these are discrete and easily forgotten.
• Conceptual understanding (physics principles, legal frameworks): Longer intervals (e.g., 3-7-14 days) because understanding deepens over time.
• Procedural skills (coding syntax, surgical techniques): A mix—short intervals for the steps, longer intervals for the overall process.

The best approach is to create separate decks for each subject type and customize the intervals per deck. SpaceRep's interval customization feature makes this easy.

What Is the 1-7-16-35 Day Interval Schedule?

This classic schedule, popularized by SuperMemo's Piotr Wozniak, is one of the most researched interval patterns. The numbers represent days between reviews: 1, 7, 16, 35. According to SuperMemo's data, this schedule can increase recall from around 30% to over 80% after one month.

It works best for moderately difficult factual material—think medical terminology, historical dates, or legal definitions. For very easy or very hard content, you'll need to adjust. The key is that the intervals grow exponentially, not linearly, which mirrors the forgetting curve.

How Often Should I Review Cards That I Find Very Easy?

For very easy cards, you can increase the interval significantly—2x or 3x the default—to avoid over-reviewing. Most SRS apps, including Anki and SpaceRep, allow you to mark a card as "easy" to automatically increase its interval. This prevents you from wasting time on material you've already mastered.

A good rule of thumb: if you can recall a card correctly three times in a row without hesitation, consider increasing its interval by 50-100%. The goal is to spend your review time on the edges of your knowledge, not on the comfortable center.

Practical Checklist for Setting Up Your First Interval System

Ready to implement? Here's a step-by-step checklist:

1. Choose your base schedule: Start with 1-3-7-14-30 days for most content.
2. Create subject-specific decks: Separate factual, conceptual, and procedural material.
3. Set your learning steps: In Anki, use 1 10 (minutes) for initial learning.
4. Adjust graduating interval: Start at 1 day, increase to 2-3 days if you're breezing through.
5. Set a maximum interval: 365 days is a safe default; increase for very stable knowledge.
6. Monitor your recall rate: Aim for 80-90% correct. If you're above 90%, increase intervals. Below 70%, shorten them.
7. Use "easy" and "hard" buttons: Let the algorithm adapt to your performance.
8. Review weekly: Check your deck statistics and adjust settings as needed.

Compare SRS apps to find the one that best supports your interval strategy.

Frequently Asked Questions About Spaced Repetition Intervals

What are the best spaced repetition intervals for language learning?

A common starting schedule is 1 day, 3 days, 7 days, 14 days, 1 month, then 2 months. Adjust based on your recall success rate.

How do I customize intervals in Anki?

In Anki, go to the deck options and adjust the 'Steps (in minutes)' and 'Graduating interval', 'Easy interval', and 'Maximum interval' settings under the 'Reviews' tab.

Should I use the same intervals for all subjects?

No. For factual material (e.g., dates, definitions), shorter initial intervals work better. For conceptual understanding, longer intervals may be more effective.

What is the forgetting curve and how does it relate to intervals?

The forgetting curve shows how quickly we forget information over time. Spaced repetition intervals are designed to review material just before you would forget it, strengthening memory.

How often should I review cards that I find very easy?

For very easy cards, you can increase the interval significantly (e.g., 2x or 3x the default) to avoid over-reviewing. Most apps allow you to mark a card as 'easy' to automatically increase its interval.

Ready to Put These Intervals Into Practice?

The science is clear: the right intervals can transform your retention from fragile to rock-solid. But knowing the theory is only half the battle—you need a tool that makes it easy to implement.

SpaceRep handles the complex scheduling math for you, adapting intervals in real-time based on your performance. No more manual calculations or spreadsheet tracking. Just show up, review, and watch your knowledge compound.