Simple vs Compound Interest with Real TZS Amounts
The difference between simple vs compound interest is what happens after the first interest amount appears. Simple interest keeps using the original amount. Compound interest adds the interest to the balance, then uses that larger balance next time.
The tables below show the effect in Tanzanian shillings, step by step. They are illustrations, not product quotes.
Simple interest: the original amount stays in charge
Imagine TZS 100,000 earns simple interest of 10% a year. The interest is based only on the original TZS 100,000, so the account adds TZS 10,000 each year.
| End of year | Original amount | Interest added that year | Total amount |
|---|---|---|---|
| 1 | TZS 100,000 | TZS 10,000 | TZS 110,000 |
| 2 | TZS 100,000 | TZS 10,000 | TZS 120,000 |
| 3 | TZS 100,000 | TZS 10,000 | TZS 130,000 |
The annual addition stays TZS 10,000. After three years, TZS 30,000 has been added.
This assumes the interest earns no interest. A real product may pay it out or use different terms. Check how the provider defines and applies the rate.
Compound interest: the same step uses a larger amount
Now keep the same TZS 100,000 and 10% annual rate, but leave the interest in the account. Year one is identical. Year two adds TZS 11,000 because the starting balance is now TZS 110,000.
| End of year | Amount at start of year | Interest added that year | Total amount |
|---|---|---|---|
| 1 | TZS 100,000 | TZS 10,000 | TZS 110,000 |
| 2 | TZS 110,000 | TZS 11,000 | TZS 121,000 |
| 3 | TZS 121,000 | TZS 12,100 | TZS 133,100 |
Compound interest is the same action repeated on a larger number. The Consumer Financial Protection Bureau describes it as earning interest on your savings and on the interest already earned.
Simple vs compound interest over ten years
Here is the same TZS 100,000, the same 10% annual rate and no extra deposits or withdrawals. Compound interest is applied once a year. Amounts are rounded to the nearest shilling.
| Time passed | Simple interest total | Compound interest total | Difference |
|---|---|---|---|
| 1 year | TZS 110,000 | TZS 110,000 | TZS 0 |
| 3 years | TZS 130,000 | TZS 133,100 | TZS 3,100 |
| 5 years | TZS 150,000 | TZS 161,051 | TZS 11,051 |
| 10 years | TZS 200,000 | TZS 259,374 | TZS 59,374 |
The gap starts small and widens as accumulated interest earns more interest. Investor.gov describes the same effect.
These totals ignore fees, tax, inflation and rate changes, and assume all interest remains in place. Withdrawing it reduces future compounding.
On a loan, compounding works against the borrower
The mechanism does not change when the balance is debt. If unpaid interest or a charge is added to what you owe and the next charge applies to that larger balance, the debt compounds.
Consider a hypothetical TZS 500,000 balance charged 10% at the end of each period, with no repayment:
| End of period | Simple-charge balance | Compound-charge balance |
|---|---|---|
| 1 | TZS 550,000 | TZS 550,000 |
| 2 | TZS 600,000 | TZS 605,000 |
| 3 | TZS 650,000 | TZS 665,500 |
The simple version adds TZS 50,000 each period. Compound charges grow because earlier charges join the balance.
Ask whether interest or penalties can attract further charges. Check the calculation base, timing and total repayment. Compare scenarios with the JengaWealth loan calculator.
What the TZS 580,277 mobile-loan case proves—and does not
In our mobile-loan example, a borrower told The Citizen that he received TZS 580,277 and saw TZS 77,397 in interest added within hours. The implied balance is TZS 657,674.
The report does not identify the loan’s calculation method or establish that another charge was applied to the larger balance. It would therefore be wrong to call the reported TZS 77,397 itself proof of compounding.
If the same proportional charge were later applied to TZS 657,674, it would add about TZS 87,720, reaching TZS 745,394. That step is hypothetical, not the borrower’s reported outcome.
The lesson is to inspect the agreement. Tanzania’s Financial Consumer Protection Regulations require disclosure of the total cost of credit, including principal, interest and third-party charges.
Why compounding frequency changes the amount
“12% per year” does not by itself tell you how often interest is added. The next table keeps TZS 100,000 and the stated annual rate at 12%, but changes how often compounding occurs during one year.
| Interest added | Amount after one year |
|---|---|
| Once a year | TZS 112,000 |
| Every three months | TZS 112,551 |
| Every month | TZS 112,683 |
| Every day | TZS 112,747 |
More frequent compounding produces a larger amount because interest joins the balance sooner. On savings it can increase earnings; on debt it can increase what you owe. Compare effective annual returns or total repayments over the same period.
Why the examples are deliberately visual
FinScope Tanzania 2023 found that 56% of the assessed 2023 sample demonstrated division, while 44% did not. The assessment excluded 17% of the overall sample who chose to use a calculator, an option not offered in 2017. The report recommends more visual, example-led financial communication.
This is the single piece of arithmetic behind both saving and borrowing: does the next interest amount use the original number, or the new balance?
Frequently asked questions
What is simple interest in plain language?
Simple interest is calculated from the original amount. In the example above, TZS 100,000 at 10% adds the same TZS 10,000 each year.
What is compound interest in plain language?
Compound interest applies to the original amount plus interest already added. The number used for the next interest amount therefore grows.
Is compound interest always good?
No. It can help savings grow when interest stays invested, but it can make unpaid debt grow faster.
Does a higher compounding frequency matter?
Yes. With the same stated annual rate, adding interest more frequently changes the final amount. Compare effective returns or total repayments, not the rate alone.
Are the TZS examples guaranteed returns or actual loan offers?
No. They are educational illustrations. Real outcomes depend on product terms, fees, tax, repayments, withdrawals and rate changes.
Read the balance, not just the rate
Simple and compound interest can begin with the same rate and first-year result. The difference appears next time. Follow the balance period by period and check whether earlier interest stays separate or joins the amount used next. That habit works for money saved and money owed.
Last updated: August 2026.