All calculators.

Map out each possible outcome, guess the odds, and get a single expected-value score that captures how the decision likely plays out on average.

• ·Decisions with meaningful uncertainty
• ·When you can estimate probabilities
• ·Big emotional outcomes you're nervous about

A weighted pros-and-cons list. Assign each reason an importance score so the loudest voice doesn't drown out the most important one.

• ·When you already have a list of reasons
• ·Weighing qualitative trade-offs
• ·Decisions where probabilities feel like overkill

Net Present Value, benefit-cost ratio, and payback period for decisions that play out over time. Optionally discount future cash flows.

• ·Money-centered decisions
• ·Costs and benefits over multiple years
• ·Comparing the return of one path

Combine a prior probability with a test's true- and false-positive rates to get the posterior probability — what to actually believe after seeing the evidence.

• ·Reading a positive test result
• ·Updating a belief when new evidence arrives
• ·Sanity-checking 'X% accurate' claims