Each calculator on this site states its formula and names its source. These guides are the longer version: what the convention actually means, why two lenders can quote different numbers for the same loan, and which rule decides it when they disagree.
Nothing here recommends a course of action. That is the same rule the calculators follow, and it is deliberate: the arithmetic is checkable and your circumstances are not something this site can see.
Debt
What a balance costs to carry, and how long it takes to clear.
4 guides
- How credit card minimum payments are calculated Issuers use two different minimum payment formulas, and the one yours uses changes your payoff date by years. This is both of them, worked through.
- Why two payoff calculators give you different answers Run the same balance through two sites and you get two payoff dates. Neither has to be wrong. This is what they are each assuming, and how to tell which matches your card.
- Snowball and avalanche, and what actually differs Both methods pay every minimum and put the surplus on one debt. The only difference is which debt, and that difference is smaller than it is usually made to sound.
- Why you still pay interest after paying the balance in full You cleared the card and the next statement still charged interest. That is residual interest, it is not an error, and the grace period is what decides whether you see it.
Mortgage
Recasting, releasing equity, and paying down early.
8 guides
- What an amortisation schedule shows Why the early payments on a mortgage are almost all interest, why the balance barely moves for years, and how to read the table that proves it.
- Recasting and refinancing are not the same thing A recast keeps your rate, your term and your loan, and only lowers the payment. A refinance replaces the loan entirely. The difference decides which one is even available to you.
- How an extra mortgage payment gets misapplied Sending extra money does not automatically reduce your principal. Servicers have three different default behaviours, and two of them waste the payment.
- When PMI comes off, and who decides Two thresholds, two different rules, and both measured against the price you originally paid rather than what the home is worth now.
- What the caps on an adjustable rate mortgage mean A 5/1 ARM with 2/2/5 caps has a worst case you can calculate exactly. This is how the three numbers work and what the ceiling actually is.
- What happens when a HELOC draw period ends The payment on a home equity line can more than double overnight, and the date it happens is in your agreement. This is the arithmetic behind the jump.
- Why a short-term loan rate looks small and is not A 2% fee on a six-month bridge loan is not a 2% rate. Annualising it is the only way to compare it with anything else, and the number that comes out is usually a surprise.
- What an interest-only payment leaves behind Ten years of interest-only payments on a home equity line leaves the balance exactly where it started. This is what that costs, worked through.
Savings
What a deposit grows to, and how long a pot lasts.
7 guides
- APR and APY are not the same number One ignores compounding and one includes it. Which you are quoted depends on whether you are borrowing or saving, and the gap widens as the rate rises.
- What breaking a CD early actually costs The penalty is quoted as a number of months of interest, so it can exceed what the certificate has earned and take a bite out of your deposit.
- How FDIC insurance limits actually work The 250,000 dollar limit is per depositor, per bank, per ownership category, and that last phrase is the one that decides how much of your money is covered.
- Is savings interest taxable, and what that does to your real return Interest is ordinary income, taxed at your marginal rate, and reported on a 1099-INT. The after-tax yield is the only one worth comparing against inflation.
- What a CD ladder trades away, and what it buys A ladder earns less than putting everything in the longest term. That shortfall is the price of never being forced to break a certificate early, and it is measurable.
- What compounding frequency is actually worth Daily compounding sounds better than monthly and is worth about a hundredth of a percentage point. The rate itself is worth twenty times more, and it is the thing to compare.
- A money market account and a money market fund are different products One is a bank deposit with FDIC insurance. The other is an investment that can lose value. The names are nearly identical and the protections are not.
College
Saving for education costs that are years out.
2 guides
- How a Pell Grant award is worked out The formula is short, the order matters, and the Student Aid Index replaced the Expected Family Contribution in 2024-25. This is the calculation in sequence.
- What a 529 does to financial aid A parent-owned 529 is assessed at up to 5.64 percent as a parental asset, not at 20 percent as a student asset. Who owns the account changes the arithmetic.