Meet Challenge Rated: A Balanced Encounter-Building Calculator

Challenge Rated is the webtool version (built by open-source contributors) of my Challenge Ratings 2.0 encounter-building system. It uses a custom algorithm, using benchmarked monster and player statistics, to estimate the amount of hit points and resources the players will need to spend in a given encounter—thereby allowing DMs to build balanced, curated encounters and adventuring days to meaningfully challenge their players without risking a TPK.



It does so by mathematically solving the “action economy” problem (which you can read more about here), leaving it robust to parties of any size or level—including, as one playtester discovered, a six-player, 20th-level party with multiple NPC allies of differing Challenge Ratings and multiple simultaneous bosses. It can also handle multi-phase boss monsters and multiple discrete waves of enemies.

I’ve been working to develop this tool since publishing the original encounter-building formula nearly two years ago, making sure it has an easy-to-use interface and refining the algorithm and benchmarks to ensure it’s accurate. I’ve also playtested it among a substantial number of DMs, including in my own 8+ person campaign, and found it to be a reliable predictor of encounter difficulty. I’ve used it in my rework of Curse of Strahd, including with multi-phase boss encounters that readers tell me are well-balanced and highly tense—but without a high risk of TPK.

I won’t oversell it, though—it’s not a panacea. The algorithm models combat as a meatbag slugfest, assuming a white-room, DPR-driven fight with no tactics or environmental features. It can’t fully account for the variance of the dice, which—especially given how short most encounters are—can cause swings in difficulty in either direction. It can’t handle monsters whose official Challenge Ratings are miscalculated or misleading (of which there are several). It doesn’t model players who make suboptimal decisions, or who have overpowered spells or magic items. And it can’t handle overlapping waves of enemies—at least, not yet.

D&D combat is a big, messy, beautiful mosaic. No calculator or simulator could ever perfectly predict it—the best we can do is approximate. But hopefully this tool’s approximations can, if nothing else, provide a reasonable foundation to build upon.

Note that this is still technically a beta release, not a full release. We’re actively looking to add new features to the site, including an encounter generator for different types of combats, an “encounter adjuster” that holds a given encounter’s difficulty constant for parties of different levels or sizes, and a general design overhaul. We’d also eventually like to release a statblock builder/CR calculator to accompany it that dynamically and accurately calculates Challenge Ratings using tweaked guidelines from the DMG and lessons learned from experimenting with monster design.

To that end, if you’re a front-end or back-end web developer interested in supporting this (open-source) project, feel free to shoot me a DM! All help is welcome and sincerely appreciated. And if you’re not a developer, we still welcome your feedback, suggestions, and critiques via the site’s feedback form or here in the comments.

Thank you very much for trying our tool out—I hope it proves helpful in your campaigns! You can click here to try it out.

(PS: Expect a new Reloaded release tomorrow or Friday 👀 🦇)