English how-to · updated 2026
The savings-and-loan search that shows up in every personal-finance class. This page has 50 important questions and answers. Original explainer for daily search — not a government login or live tracker.
Simple interest is earned only on the original principal. Compound interest is earned on the principal plus interest already added — interest on interest. The more often it compounds (yearly, monthly, daily), the faster a balance can grow — or a debt can swell.
Credit cards and some student loans compound. Savings accounts and index funds use the same maths in the other direction. The Rule of 72 is a rough “years to double” shortcut: 72 ÷ annual % rate.
50 important questions. Quick 10 is a random set; Full set plays every question.
Original explainers for English readers — not copied match reports or official papers. Tap a question to see the answer.
Answer: interest on principal plus earlier interest
That is why time in the market matters.
Answer: the original principal only
It grows in a straight line.
Answer: a standard compound-interest formula
P is principal, r is the annual rate.
Answer: 9 years
72 ÷ 8 = 9.
Answer: grows a savings balance a bit faster
Read the APY, not only the APR.
Answer: can grow a unpaid balance quickly
Pay more than the minimum when you can.
Answer: time lets compounding work longer
Small regular amounts still add up.
Answer: the same as inflation, though both use percents
Inflation can eat real returns.
Answer: the starting amount before interest is added
Interest is calculated on this, then on more if it compounds.
Answer: includes the effect of compounding
Compare APY when shopping savings.
Answer: usually produces a slightly higher effective yield
Banks quote both figures for a reason.
Answer: can see the balance stall or even grow
That is how card debt swells.
Answer: 12 years
72 divided by 6 is 12.
Answer: 8 years
72 divided by 9 is 8.
Answer: 6 years
It is a shortcut, not a bank contract.
Answer: 300 of interest (100 a year)
Compound would add interest on the 100s too.
Answer: 1331
1000 x 1.1 x 1.1 x 1.1 = 1331.
Answer: what you actually earn or pay in a year after compounding
It lets you compare odd compounding schedules.
Answer: the mathematical limit of compounding ever more often
The formula uses e to the power rt.
Answer: the real growth of savings can be much smaller than the nominal
A 5% APY with 5% inflation is about zero real.
Answer: more periods exist for interest to land on interest
Time is the hidden multiplier.
Answer: a modest rate left to compound for many years
Charts of long horizons make this obvious.
Answer: daily wins by a small extra yield
Read the APY line.
Answer: add unpaid interest to the principal
Ask when capitalisation happens.
Answer: payments above the interest being added
Minimums often barely cover interest.
Answer: incomplete for a fair comparison
Ask how often it compounds.
Answer: compound interest back into simple on a flat principal
The pot stops growing by interest-on-interest.
Answer: compound the wrong way and shrink a balance
Read the tariff.
Answer: rates are extreme or compounding is very frequent and you need precision
Use the real formula for contracts.
Answer: today money equivalent of a future compounded sum
Discounting is compounding in reverse.
Answer: a stream of payments earning interest as they sit
Pensions and regular savers use this idea.
Answer: raise the rate or compound more often
Or add fresh principal.
Answer: compounds, so the yearly cost is higher than month x 12 in simple terms
The APR/EAR box is the honest comparison.
Answer: guarantee a 4% rise in real buying power
Inflation and tax sit in the middle.
Answer: compounding if they buy more units
Spending the dividends stops that path.
Answer: how many compounding periods in t years
n is compounds per year; t is years.
Answer: P
No rate, no growth from interest.
Answer: waiting to repay can cost more than the original spend
Time works against the borrower.
Answer: can change the compounding path after the honeymoon
Read the revert rate.
Answer: new principal that will itself start compounding
Regular contributions dwarf a one-off for many people.
Answer: the one with the prettier advertised headline rate
Fees compound too — against you.
Answer: is not the same as 5% a year for two years
Order and compounding both matter.
Answer: slow compounding if you cannot shelter the account
Use legal wrappers if they exist where you live.
Answer: approximates the annual effective yield for that APR
That is what n = 4 means.
Answer: the compounded sum you will not have later
That is why payday transfers help.
Answer: you leave the interest invested (or unpaid, on a loan)
Withdrawals break the assumption.
Answer: it can fit continuous or frequent compounding a bit better
Classroom Rule of 72 is still the usual shortcut.
Answer: usually ends far ahead even at the same rate
The extra years are extra compounds.
Answer: compound interest
That is the whole idea.
Answer: whether the rate is per year and how many times it compounds
Underline n and t first.
Pick the next article in this topic — that is how a magazine issue is meant to be used.
