Help me
decide.
Free calculators for real-life decisions. Run the numbers on risky choices, weigh what matters, and make peace with tough calls.
Which calculator fits?
Answer a few quick questions and we'll point you at the right tool.
What's the decision mostly about?
Pick the closest fit — there are no wrong answers.
Pick the one that fits the question.
Each one is free, works offline, and doesn't send your decisions anywhere.
Expected Value
Run the numbers on risky decisions.
- ·Decisions with meaningful uncertainty
- ·When you can estimate probabilities
- ·Big emotional outcomes you're nervous about
Pros & Cons
Weigh what matters, not just what's loudest.
- ·When you already have a list of reasons
- ·Weighing qualitative trade-offs
- ·Decisions where probabilities feel like overkill
Cost–Benefit
Does it pay off in dollars and years?
- ·Money-centered decisions
- ·Costs and benefits over multiple years
- ·Comparing the return of one path
Bayesian
Update your belief when new evidence arrives.
- ·Reading a positive test result
- ·Updating a belief when new evidence arrives
- ·Sanity-checking 'X% accurate' claims
Math, honest about its limits.
Most decisions don't need a calculator. The ones that do — big moves, money questions, scary conversations — are exactly the ones your gut is worst at. Not because the gut is wrong, but because it's running the math in your head without writing anything down.
This site is a set of small tools that make the math visible. Expected value for risky decisions. A weighted pros-and-cons list when you already have a list. Cost-benefit analysis for anything that plays out over years.
None of this replaces your judgment. It just gives your judgment something honest to argue with.
From the notebook.
All essaysMay 11, 2026
What a Positive Test Really Means
A 99% accurate test comes back positive. Most people assume they're 99% likely to have the disease. The real answer is closer to 9% — and the math is easier than it looks.
July 19, 2025
Why Future Dollars Count for Less
A dollar next year isn't worth a dollar today. Discount rates, NPV, and the surprisingly emotional math of decisions that play out over time.
June 3, 2025
Weight, Not Length: A Better Pros and Cons List
An unweighted pros-and-cons list rewards whoever can think of the most reasons, not whoever has the most important ones. Here's how to fix it.