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Why I built this

About TheSharpDollar

I learned the value of a dollar early, back when I didn't have many of them. When money is finite, you get resourceful fast. You learn to stretch every dollar, and to weigh what you give up against what you get for it. What I figured out young, and still believe, is that the goal was to get the most life out of what I had, not to spend less. That meant optimizing for happiness and value at the same time. That way of thinking has shaped almost every decision I've made in the decades since.

I come from an engineering background, and I've been a numbers person for as long as I can remember. I like taking a decision apart, breaking it down, and seeing what the math says. Because numbers don't lie, but the stories we tell ourselves about them do it all the time.

The more decisions I ran the numbers on, the more I kept seeing the same thing: we're constantly misled about how to think about the things we buy. We all want the newest, shiniest version of everything, and that's human. But once you look at how something actually serves you, the math changes completely. Measure it in cost per mile, cost per use, or cost per year, and the picture looks nothing like the sticker price.

I've always chased value, and not just the financial kind. I care whether the things I commit to fit the life I'm building. So with almost any decision, I catch myself asking the same questions: Does this help me today? Will it still make sense in five years? Sometimes I'll measure it in cost per use, cost per hour, even fun per dollar. Your priorities shift and your circumstances change, and what counts as a good decision should shift right along with them. You're going to spend the money either way. The only question is whether you got what you wanted for it.

Somewhere along the way, I became the person friends and family came to before a big money move. Should I buy or lease, refinance now or wait, take the job that pays more but costs me the commute. I'd do the due diligence and crunch the numbers, then lay the comparisons out plainly and let them make the call. I never wanted to tell anyone what to do. I just wanted them to see it clearly.

I couldn't find a tool that did that, both easy to use and completely free, with nothing being sold to me inside the tool. So I built TheSharpDollar, first as the thing I wished I could hand each of them, and then as something to share with you too. It's just me behind it, but I couldn't have made it happen without the friends and family who tested it, poked holes in it, and told me when I was wrong.


How I think about spending

Spending is a form of choosing. What matters is knowing what something costs you and deciding whether it's worth it, which sometimes means spending more.

So the calculators give you the arithmetic and leave the decision to you. If two options come out close, the result says so instead of picking one. Anything that depends on your own plans, like how long you expect to stay in a house, is an input you fill in yourself.


Why it asks for your numbers

Most personal finance advice is written for an average person who doesn't exist. A mortgage that suits someone staying thirty years can be a bad deal for someone moving in five, and a sensible car budget depends on how far you drive and what your insurance costs. Details like that change the answer.

So every calculator here starts from your figures. Two people can open the same one, type in their own situation, and walk out with opposite answers that are both correct.


Why I keep working on it

People who understand the math make different money decisions from people who don't, and it has surprisingly little to do with income. They can tell when a low monthly payment hides a bad deal, and they know the difference between something that loses value and something that compounds. Most of all, they know how much time is worth.

That kind of understanding usually comes from a paid advisor or years of reading. Very little of it is hard once someone shows you the working, which is why most of the calculators here show theirs.


What's under the hood

TheSharpDollar has 39 calculators across six categories: Savings & Investing, Retirement, Automotive, Housing, Credit Cards & Loans, and Work & Life. They use standard formulas (loan amortization, present value, compound growth) and show their key assumptions. They're planning estimates for learning, not personalized financial advice.

Compound interest is calculated period by period. Retirement projections work in today's dollars using a real (inflation-adjusted) return. Social Security comparisons take the benefit estimate from your SSA statement and apply the agency's early-claim reduction and delayed-retirement-credit rules to compare claiming at 62, your full retirement age, and 70. They do not recompute your benefit from your earnings record. Mortgage amortization builds a full payment-by-payment schedule. Loan comparisons look at the total cost over the life of the loan as well as the monthly payment.

The calculators run in your browser. There's no account or sign-in, and what you type isn't sent to a server. The only thing recorded is that a calculation happened, which is what the counter on the homepage shows. The numbers you enter are never seen.


How this is paid for

Keeping this free still costs money. That may come from ads on my YouTube videos, a few ads here, or referral links, where a company pays me if you sign up through one, at no cost to you.

None of that changes the math. The calculators work the same way for everyone. Thirty-five of the 39 calculators show their formulas under "Show the math" if you want to check. When I find a mistake, the fix is listed in the changelog.

Open the Calculators

On YouTube

I also work through these decisions on YouTube, one person and one decision per video, with the calculator on screen. Subscribe to @TheSharpDollar to see each one worked through before you have to make it yourself.

Watch on YouTube

Get in touch

Questions, feedback and business ideas are all welcome. I read every message and try to reply to all of them.


Unlike the calculators, this form sends what you type to me when you press Send.