FirstGenFinance@firstgenfinanceELI5: how does compound interest actually work? Everyone says 'it's interest on interest' and I nod like I get it
I understand that if I put in $100 and earn 5%, I have $105. What I don't get is why people act like it's magic over time. It's the 'interest on interest' part that my brain slides right off of. Small words please.
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thesispending@thesispending· 7/4/2026, 6:00:24 AMThink of it like a snowball rolling downhill. Year one, your $100 earns $5 — small snowball. But year two, you don't earn 5% on the original $100, you earn it on $105. So you make $5.25. Tiny difference, right? The trick is that the extra bit gets added to the ball every single year, and next year IT earns too. The snowball grows the hill it's rolling down. The magic isn't in any one year. It's that the growth compounds on itself, so the line curves upward instead of going straight. Give it 30 years and that curve gets genuinely silly.
FirstGenFinance@firstgenfinance· 7/4/2026, 6:54:41 AMThe snowball is the thing that finally clicked. Each year's gain becomes next year's seed. Okay, that's actually kind of beautiful and slightly infuriating that nobody explained it this way in school.
GalaxyBrainGwen@galaxybraingwen· 7/4/2026, 6:41:27 AMThere's a shortcut you'll love: the Rule of 72. Take 72, divide it by your interest rate, and you get roughly how many years it takes your money to double. At 6%, that's 72/6 = about 12 years to double. At 8%, about 9 years. It's an approximation, not a law of physics, but it's close enough to do in your head and it makes the 'why start early' argument obvious.
IndexFundIrene@indexfundirene· 7/4/2026, 9:31:06 AMThe unglamorous truth from the personal finance side: the biggest lever isn't the rate, it's time. A modest return running for 30 years beats a great return running for 10. That's the whole reason 'start now with a little' beats 'start later with a lot.' Boring money, long runway.
GalaxyBrainGwen@galaxybraingwen· 7/7/2026, 11:50:01 PMComing back to add the depressing/motivating flip side of compound interest: it works exactly the same way on debt. Credit card balances snowball uphill against you at scary rates. Same math, opposite direction — which is why 'pay it off early' and 'start saving early' are really the same piece of advice.