How does the fixed deposit calculator work?
A fixed deposit is a deposit where you lock your money for a set period in exchange for an interest rate known in advance. Enter the principal, the Annual Nominal Rate (APR) and the number of days, and the calculator shows the interest you will earn and the total amount you will collect at maturity.
Fixed deposit formula
Final amount = Principal + Interest
Worked example
You deposit 10,000,000 at a 30% APR for 90 days:
- Interest = 10,000,000 × 0.30 × (90/365) = 739,726
- Final amount = 10,000,000 + 739,726 = 10,739,726
If you extended that same deposit to 365 days at the same rate, the interest would be 3,000,000 and the final amount 13,000,000.
How to get more out of a fixed deposit
- Compare the APR between banks: a few points of difference change the result a lot on large amounts.
- Renew with interest: by renewing including the interest earned, you start to compound and speed up growth.
- Look at the real rate: subtract expected inflation from the APR to know your true gain.
- Ladder your terms: splitting the principal into several deposits with different maturities gives you liquidity without losing yield.
Frequently asked questions about fixed deposits
Most banks use simple interest for a single term: interest = principal × (APR/100) × (days/365). The final amount is the principal plus that interest. This calculator applies exactly that formula on a 365-day year basis.
The APR (Annual Nominal Rate, or TNA in Spanish) is the rate the bank offers for one year, without considering reinvestment. For a term shorter than a year it applies proportionally to the days. Do not confuse it with the EAR, which does account for compounding.
It depends on the context. In economies with inflation or variable rates, short terms give you flexibility to renew at a new rate. Long terms lock in the current rate, which is good if you expect rates to fall. Always compare the APR offered for each term.
Only if the APR exceeds the inflation rate for the period. If annual inflation is 25% and your deposit pays 30%, you gain in real terms. If it pays 20%, you lose purchasing power even though the number grows. Always compare rate against expected inflation.
In general a traditional fixed deposit locks the money until maturity. Some banks offer pre-cancelable deposits, but they usually pay a lower rate. Read the terms before depositing if you think you will need liquidity.