Compound Interest Calculator — Monthly Savings, DCA & Inflation

How it works

Enter your starting amount, how much you will add each month, the expected annual return and the number of years. You get the final balance, split into money deposited and returns earned. Add inflation to see the value in today’s money.

Formula

Lump sum: balance = principal × (1 + r ÷ n)^{n × years}, where n = compounding periods per year

Monthly deposits: balance = deposit × ((1 + i)^months − 1) ÷ i, where i = equivalent monthly return (deposits at month end)

Real value = balance ÷ (1 + inflation)^years

How compound interest works

Compound interest adds the interest you earn to your balance, so the next period’s interest is calculated on a bigger amount. Growth speeds up over time, unlike simple interest, which is only paid on the original amount.

The most powerful factor is time. Starting 10 years earlier often matters more than saving twice as much later.

What 1,000 baht a month grows to

Return per year	10 years	20 years	30 years
2%	132,720	294,797	492,725
4%	147,250	366,775	694,049
6%	163,879	462,041	1,004,515
8%	182,946	589,020	1,490,359

(Compounded monthly, deposits at month end. Actual money deposited: 120,000 / 240,000 / 360,000 baht.)

Saving 1,000 baht a month for 30 years at 6% gives over 1 million baht, though you put in only 360,000. The rest comes purely from compounding.

The rule of 72: years to double your money

Divide 72 by the annual return:

2% a year: about 36 years
4% a year: about 18 years
6% a year: about 12 years
8% a year: about 9 years

Don’t forget inflation

Inflation means the same money buys less over time. With 2% inflation, 1 million baht in 20 years is worth about 673,000 baht today. Enter inflation in the calculator to see the real value.

Your real return is roughly return − inflation. A savings account paying less than inflation loses value every year.

Rough returns by type

Past returns don’t guarantee future ones. These are only rough ranges to try in the calculator:

Savings accounts — low interest; check your bank’s actual rate
Fixed deposits and government bonds — low risk, slightly more than savings
Balanced or equity funds over the long term — higher average returns, but volatile, with some losing years

Tips for saving that works

Set up an automatic transfer on payday — save first, spend what’s left
Invest regularly (DCA) — reduces the risk of bad timing
Use tax deductions — saving through RMF or Thai ESG gives you a tax refund on top
Raise your savings every time your salary goes up

FAQ

What is compound interest?

Earning interest on both your money and the interest it has already earned, so growth speeds up over time. 100,000 baht at 5% a year becomes about 162,889 baht in 10 years and about 432,194 baht in 30 years.

How much will 1,000 baht a month grow to in 10 years?

At 6% a year compounded monthly, about 163,879 baht from 120,000 baht deposited. A low-interest savings account grows much less.

What is the rule of 72?

A quick way to estimate how many years it takes to double your money: divide 72 by the annual return. At 6% that is about 12 years; at 8%, about 9 years.

Why account for inflation?

Prices rise over time. With 2% inflation, 1 million baht in 20 years buys what about 673,000 baht buys today. Enter inflation to see your future balance in today’s money.

Compound Interest & Savings Calculator