Interest Calculator
Calculate deposit or loan interest after tax, with flat, effective, annuity, compound, tiered, step-up and floating methods.
Interest Calculator
Work out interest on deposits and loans. Anything marked ID follows a convention commonly used in Indonesia; everything else is generic. Everything runs in your browser.
One rate per line (for example per year): 6, then 7, then 8. Values are percent per year. If there are more periods than lines, the last line repeats.
One bracket per line: upper_limit rate. Use * for the remainder with no upper limit. The example means the first 10 million at 3%, the next 40 million at 4%, and the rest at 5%.
Choosing a product fills in the tax and day-count basis that product usually uses in Indonesia — deposit 20%, government bond 10%, money market fund 0% — and you can change them. A tenor in months is counted as 30 days each; a year is 365 or 360 days depending on the basis.
Result
How the method works
History tool ini
Data terakhir yang pernah kamu isi di tool ini, tersimpan hanya di device/browser ini.
Save what you type here, in this browser? Your work would go into this browser's local storage, so a refresh or a trip to another tool does not wipe it. You also get a short list of previous entries under the form, each one restorable with a click. Nothing is ever uploaded, and there is no account.
Being straight about the trade-off: anything kept there can be read by anyone who can use this browser profile, and by any script that later runs on this site. A tool page can hold a private key, a password or a signed token. Saving is convenient; it is not private.
About this tool
A calculator for the interest methods that are easy to mix up: simple, compound, tiered, step-up, floating, flat, effective and annuity. Enter a principal, a rate and a tenor and the page shows the formula it used, the result as gross, tax and net where tax applies, and a period-by-period breakdown. The product presets follow the tax and day-count conventions commonly used in Indonesia and are marked ID; everything is computed in the browser.
Questions
- What is the formula for simple interest?
- I = P x r x (days / basis), where P is the principal, r the rate per year as a decimal, and basis the day count (365 or 360). The interest is paid once and never earns interest itself, which is how a deposit that pays at maturity works.
- What is the formula for compound interest?
- A = P x (1 + r / n)^(n x t), where n is the number of compounding periods per year and t the tenor in years. Each period's interest is added to the balance so the next period earns interest on it. When tax is withheld at each payment, the amount that compounds is the net interest.
- How are tiered, step-up and floating interest calculated?
- All three add up per-slice amounts instead of applying one rate to the whole balance. Tiered splits the balance into brackets and computes slice x rate x (days / basis) for each. Step-up and floating apply a list of rates per period and add P x r_i x span_i. The only difference is that step-up rises on a schedule while floating can move either way.
- What is the difference between flat, effective and annuity?
- Flat charges interest on the original principal for the whole term: I = P x r x (months / 12), split evenly across the instalments, so the true cost is higher than the headline rate. Effective charges interest on the remaining balance each month: interest = remaining x r / 12, so the interest share falls over time. Annuity keeps the total instalment fixed with A = P x i / (1 - (1 + i)^-n), where i = r / 12 and n is the number of months, while the split shifts from interest to principal.
- Why does one month not equal one twelfth of the yearly rate?
- Because the day-count basis decides how a month becomes a fraction of a year. Actual/365 counts a month as 30/365, a little less than a twelfth; 30/360 treats every month as exactly 1/12, a little more. The page lets you switch basis so the choice is visible instead of hidden.
- Which parts are specific to Indonesia?
- The product presets and the ID badges: the final tax on deposit and bond interest, the Actual/365 basis, the ARO rollover, and the loan structures quoted as flat, effective or annuity. The formulas themselves are the same everywhere; only the defaults and the naming are local.