Money doubles when the interest earned equals the amount. With compound interest, the rule of 72 gives a quick guess: 72 ÷ 12 = 6 years at 12%. Added yearly, the exact time is 6 years 1 month 10 days. At simple interest it takes 100 ÷ rate: 8 years 4 months at 12%, or 50 months at ₹2 sekda.
How many years to double money at 6% to 24%?
Exact years for money to double at common yearly rates, worked out the same way as the calculator: interest joins the principal at each rest, and the last part rest earns simple interest. The last column is the rule of 72 for comparison.
| Rate a year | Added yearly | Quarterly | Monthly | Simple interest | Rule of 72 |
|---|---|---|---|---|---|
| 6% | 11.89 | 11.64 | 11.58 | 16.67 | 12.00 |
| 7% | 10.24 | 9.99 | 9.93 | 14.29 | 10.29 |
| 7.5% | 9.58 | 9.33 | 9.27 | 13.33 | 9.60 |
| 8% | 9.01 | 8.75 | 8.69 | 12.50 | 9.00 |
| 9% | 8.04 | 7.79 | 7.73 | 11.11 | 8.00 |
| 10% | 7.26 | 7.02 | 6.96 | 10.00 | 7.20 |
| 12% | 6.11 | 5.86 | 5.80 | 8.33 | 6.00 |
| 15% | 4.96 | 4.71 | 4.65 | 6.67 | 4.80 |
| 18% | 4.18 | 3.94 | 3.88 | 5.56 | 4.00 |
| 24% | 3.20 | 2.97 | 2.92 | 4.17 | 3.00 |
So a 7% FD that adds interest every quarter doubles in 9.99 years, about 10 years; the rule of 72 says 10.29. Some sites work out log 2 ÷ log(1 + rate), which treats the last part year as compound too. That gives a few days more: 6.12 years at 12% instead of 6.11.
Try it in the calculatorA 7% FD, interest added quarterlySekda rates: months to double
| Sekda | Rate a year | Simple byaj | Added yearly | Added monthly | Effective yearly rate (monthly) |
|---|---|---|---|---|---|
| ₹1 | 12% | 100.0 | 73.3 | 69.7 | 12.68% |
| ₹1.5 | 18% | 66.7 | 50.1 | 46.6 | 19.56% |
| ₹2 | 24% | 50.0 | 38.4 | 35.0 | 26.82% |
| ₹2.5 | 30% | 40.0 | 31.3 | 28.1 | 34.49% |
| ₹3 | 36% | 33.3 | 26.7 | 23.4 | 42.58% |
| ₹5 | 60% | 20.0 | 17.0 | 14.2 | 79.59% |
At ₹2 sekda simple byaj, a loan doubles in 50 months (4 years 2 months). If the byaj is added to the principal every month, it doubles in 35 months, within 3 years, because ₹2 sekda added monthly really costs 26.82% a year, not 24%.
Try it in the calculator₹50,000 at ₹2 sekda, byaj added monthlyRule of 72, and why 72
Years to double ≈ 72 ÷ yearly rate (in %)
For compound interest. At 8%: 72 ÷ 8 = 9 years.
Money doubles when (1 + rate)^years = 2, so the exact years are log 2 ÷ log(1 + rate). The natural log of 2 is 0.693, which is why the true number sits near 70. With interest added yearly, the number that would be exact is 71.4 at 6%, 72.0 at 8% and 73.3 at 12%. So 72 fits best around 8% (exact: 9.01 years), and it divides neatly by 2, 3, 4, 6, 8, 9 and 12, which makes it easy in your head.
At high rates it runs short: at 24% it says 3 years, but with yearly interest it takes 3.20, about 2 months 14 days more. To triple money people use 114 ÷ rate (9.5 years at 12%; exact 9.68), and for 4×, 144 ÷ rate, which is just doubling twice.
Rule of 70 for monthly interest
When interest is added monthly or more often, the doubling time moves towards 69.3 ÷ rate, so 70 is the closer rule. At 12% added monthly, money doubles in 5.80 years: 70 ÷ 12 = 5.83, while 72 ÷ 12 = 6.
Doubling at simple interest: 100 ÷ rate
Years to double = 100 ÷ yearly rate; months to double = 100 ÷ sekda
With simple interest, money doubles when the interest equals the principal. At 12% a year that is 8.33 years (8 years 4 months); at ₹2 sekda, 50 months. This is also the point where the old damdupat rule, which courts in some states have applied, generally stops unpaid interest from growing any further.
Inflation halves money the same way
The rule works for prices too: at 6% inflation, prices double, so the same money buys half as much, in about 72 ÷ 6 = 12 years.
Try it in the calculatorWhat rate doubles money in 5 years?6 short answersMoney doubling and the rule of 72: quick answers
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How many years does it take to double money at 7%, 8%, 10% or 12%?
With interest added once a year, money doubles at 7% in 10 years 3 months, 8% in 9 years 1 month, 10% in 7 years 4 months, 12% in 6 years 2 months. Adding interest more often makes it a little faster: a 7% FD that compounds quarterly doubles in about 10 years. At simple interest it is slower: 100 ÷ rate, so 8.33 years at 12%.
What is the rule of 72?
The rule of 72 says compound interest doubles money in about 72 ÷ the yearly rate years. At 9% that is 8 years; with interest added yearly the exact answer is 8.04 years. It is a quick check in your head. It does not apply to simple interest, where money doubles in 100 ÷ rate years.
How accurate is the rule of 72?
Close enough for the rates people meet most. From 6% to 12% with yearly interest it is never more than 1.3 months out. At 24% it says 3 years, but yearly interest takes 3.20 years. For interest added monthly, the rule of 70 is closer: at 12% monthly the exact time is 5.80 years, and 70 ÷ 12 = 5.83.
In how many years does money double at simple interest?
When the interest equals the principal, which takes 100 ÷ the yearly rate years. At 10% that is 10 years; at 12%, 8 years 4 months. With a monthly rate, divide 100 by the sekda to get months: ₹2 sekda doubles in 50 months, ₹1.5 sekda in 66.7 months.
What interest rate doubles money in 5 or 10 years?
With interest added yearly you need 14.87% a year to double in 5 years and 7.18% to double in 10. Added monthly, 5 years needs 13.94%. At simple interest it is 20% and 10%. The rule of 72 gives 72 ÷ 5 = 14.4% and 72 ÷ 10 = 7.2%.
In how many months does money double at ₹2 sekda?
In 50 months at simple byaj, because ₹2 a month on every ₹100 adds up to ₹100 after 50 months. If the byaj is added to the principal every month, it doubles in 35 months, since ₹2 sekda compounded monthly is 26.82% a year.
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