At 2 taka per 100 a month in simple interest, any debt doubles in 50 months, or 4 years 2 months. If interest goes unpaid and is added to the principal every month, it doubles in just 35 months. Enter your rate and how interest builds up below.
taka / 100 / month
How interest builds up
Grow to
৳
= 10 thousand taka
Pick a date, or type day/month/year
Time to double
4 years 2 months
on 3 December 2030
Simple yearly rate
24%
Total months
50
Total then
৳20,000
৳10,000 at 2 taka / 100 / month (simple interest (paid separately)) will double to ৳20,000 in 4 years 2 months.
Added yearly: compounded at the yearly rate for each full year, simple in the last part-year.
Examples
Rate
How interest builds
Doubles in
2 per 100 a month
simple
4 years 2 months
2 per 100 a month
added monthly
2 years 11 months
3 per 100 a month
simple
2 years 9 months 10 days
3 per 100 a month
added yearly
2 years 2 months 21 days
1 anna per taka a month
simple
1 year 4 months
To triple at 2 per 100 a month simple takes 100 months, or 8 years 4 months.
Good to know
If interest is paid on time the debt doesn’t grow; this shows what happens when interest is left unpaid.
Bank and farm loans charge far less, so a debt takes many years to double. Look at alternatives before borrowing a large amount.
For a year-by-year view, use the interest on unpaid interest calculator.
More: why a small-sounding rate grows a debt fast
Two or three taka a month sounds small, but it is 24-36% a year. If interest isn’t paid and the lender adds it to the principal, interest is charged on interest and the debt grows even faster. Knowing when it doubles makes the cost clear before you borrow.
Many people avoid interest for religious reasons. This calculator doesn’t encourage any borrowing; it only shows the cost plainly.
Frequently asked questions
How long does it take for a debt to double?
At simple interest, months = 100 ÷ the monthly rate (%). At 2 per 100 a month that is 50 months, at 3 about 33 months 10 days, at 5 just 20 months. If unpaid interest is added to the principal it is faster still.
How much faster with interest on interest?
At 2% a month added monthly it doubles in about 35 months instead of 50. At 36% a year added yearly, in about 26 months 21 days.
How fast does one anna per taka double?
One anna per taka a month is 6.25% a month, 75% a year. At simple interest the debt doubles in only 16 months.
What is the rule of 72?
A shortcut for compound growth: 72 ÷ the yearly rate = years to double. At 12% a year, about 6 years. It is approximate; this calculator uses the exact formula.
Does it work for savings too?
Yes. The same maths shows when savings double, e.g. about 7 years 3 months at 10% a year compounded.
How long to triple?
At 2 per 100 a month simple, 100 months, or 8 years 4 months. If unpaid interest is added every month, 4 years 7 months 14 days.
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