Methodology
How FID calculates
Every FID calculator uses a published formula that you can check by hand. The same calculation code runs in your browser and on our server, and it is tested against reference values.
Common assumptions
- Returns are assumptions, not forecasts. Market-linked returns vary year to year; the calculators apply a constant rate so you can compare scenarios.
- Monthly rate. Where money moves monthly, the annual rate is divided by 12 (nominal monthly rate).
- Before tax and costs. Results ignore income tax, capital-gains tax, exit loads and stamp duty unless a calculator says otherwise.
- Future rupees. Results are not adjusted for inflation unless the calculator asks for an inflation rate.
- Rates and slabs. Tax slabs, deduction limits and government scheme rates are stored with their effective dates and official source, and are reviewed when notifications change.
SIP Calculator
Each monthly instalment is assumed to be invested at the start of the month. The annual return is converted to a monthly rate as i = annual rate ÷ 12.
Value = P × [((1 + i)n − 1) ÷ i] × (1 + i)
where P is the monthly instalment and n the number of months. Invested = P × n; gains = value − invested.
Step-up SIP Calculator
The monthly instalment is raised by the step-up percentage once every 12 months: in year k (starting at 1) it is P × (1 + s)k−1. Every instalment is invested at the start of its month and grows at i = annual rate ÷ 12.
Value = Σk=1..Y P(1 + s)k−1 × [((1 + i)12 − 1) ÷ i] × (1 + i) × (1 + i)12(Y−k)
With a 0% step-up, this equals the plain SIP result.
Lumpsum Calculator
A single amount compounds once a year at the expected annual return.
Value = P × (1 + r)t
where P is the amount invested, r the annual return and t the number of years.
SWP Calculator
Each month the balance first earns i = annual rate ÷ 12, then the withdrawal is taken (end of month). If the balance cannot cover a full withdrawal, the remainder is paid out and the plan stops.
Balance after n months = C × (1 + i)n − W × [((1 + i)n − 1) ÷ i]
where C is the starting corpus and W the monthly withdrawal. Withdrawing exactly C × i each month keeps the balance flat.
Mutual Fund Returns Calculator
For a single investment held for t years:
Absolute return = (current ÷ invested − 1) × 100CAGR = ((current ÷ invested)1/t − 1) × 100
CAGR assumes one purchase date. For SIPs or multiple purchases, XIRR is the right measure.
EMI Calculator
FID uses the standard reducing-balance method. Interest is charged monthly on the outstanding principal at i = annual rate ÷ 12.
EMI = P × i × (1 + i)n ÷ ((1 + i)n − 1)
Each month: interest = balance × i; principal repaid = EMI − interest; new balance = balance − principal repaid. The last instalment is trimmed so the balance closes at exactly zero.
Home Loan Prepayment Calculator
The current EMI is worked out from the outstanding principal, rate and remaining tenure. The one-time prepayment reduces the principal immediately. Then:
- Reduce tenure: the EMI stays the same (plus any monthly extra) and the schedule runs until the balance reaches zero.
- Reduce EMI: a new EMI is calculated on the lower principal over the same remaining tenure.
Interest saved = total interest on the current schedule − total interest on the new schedule.
Income Tax & Take-home Salary Calculator
Both regimes are computed for the selected financial year using slabs, limits and rates stored with their official source.
- New regime: taxable income = gross income − standard deduction (salaried only).
- Old regime: taxable income = gross income − standard deduction − professional tax − HRA exemption − Chapter VI-A deductions. 80C (including your EPF contribution), 80D, 80CCD(1B) and home-loan interest are capped at their limits.
- Tax is applied slab by slab. The Section 87A rebate applies up to the rebate income limit; under the new regime, marginal relief limits tax just above that limit to the income exceeding it.
- Surcharge applies above ₹50 lakh with marginal relief, then 4% health & education cess on tax plus surcharge.
Monthly take-home = (gross salary − tax − your EPF − professional tax) ÷ 12.
Financial Health Score
FID's health score is our own transparent model. Five areas are each scored 0–100 on a straight line between a starting point and a target, then weighted:
- Savings rate (25%) — (income − expenses − EMIs) ÷ income. 0% scores 0; 30% or more scores 100.
- EMIs vs income (20%) — EMIs ÷ income. 20% or less scores 100; 50% or more scores 0.
- Emergency fund (20%) — liquid savings ÷ monthly (expenses + EMIs). 6 months or more scores 100.
- Insurance (15%) — average of life cover (10× annual income scores 100; full marks if no one depends on you) and health cover (₹5 lakh or more scores 100).
- Investment rate (20%) — monthly investments ÷ income. 20% or more scores 100.
Bands: 80+ strong, 60–79 steady, 40–59 needs attention, below 40 at risk. In your FID account, the inputs come from your transactions (average of the last three full months), loans, holdings and insurance details.
Retirement & FIRE Planner
Today's monthly expenses are grown by inflation to your retirement age. The corpus needed is the present value, at retirement, of yearly withdrawals that rise with inflation until the age you plan for, taken at the start of each year:
Corpus = A × [1 − ((1 + g) ÷ (1 + r))R] ÷ (r − g) × (1 + r)
where A is the first year's expenses, g inflation, r the after-retirement return and R years in retirement. Current savings grow at the pre-retirement return; monthly investments grow like a SIP. The FIRE number is annual expenses ÷ withdrawal rate, and the FIRE age is the first year your projected savings reach that year's FIRE number.
Opportunity Cost Calculator
A one-time amount is treated as a lumpsum compounding yearly. A recurring amount is converted to a monthly figure (daily × 365 ÷ 12, weekly × 52 ÷ 12) and treated as a SIP invested at the start of each month at the chosen return. "Growth you give up" is the future value minus the total spent.
FD Calculator
Maturity = P × (1 + r ÷ n)n × t
where n is the number of compounding periods per year (4 for quarterly), r the annual rate and t the tenure in years. Values are before TDS and income tax.
RD Calculator
Each monthly instalment earns interest compounded quarterly for the months it remains deposited:
Maturity = Σk=1..N R × (1 + r ÷ 4)(N − k + 1) ÷ 3
where R is the monthly deposit and N the number of months.
PPF Calculator
The yearly deposit is assumed to be made at the start of each financial year, and interest compounds annually:
Balancey = (Balancey−1 + deposit) × (1 + r)
The default rate is the current notified PPF rate from FID's rates table, with its effective period shown under the field.
EPF Calculator
Each month: employee contribution = 12% of basic + DA; employer EPF share = 12% of basic + DA − 8.33% of basic + DA (capped at the EPS wage ceiling). Interest for each month is the opening balance × annual rate ÷ 12; the year's interest is credited at year end. Basic + DA grows by the yearly increase you enter.
Sukanya Samriddhi Calculator
Deposits are made at the start of each year for the first 15 years. The balance compounds annually at the SSY rate until maturity, 21 years after the account is opened. The default rate is the current notified rate from FID's rates table.
Simple & Compound Interest Calculator
Simple: A = P × (1 + r × t)Compound: A = P × (1 + r ÷ n)n × t
XIRR Calculator
XIRR is the annual rate r that makes the present value of all cash flows zero:
Σ amountk ÷ (1 + r)daysk ÷ 365 = 0
FID solves it with Newton's method and falls back to bisection when needed. Days are counted from the first cash flow. Results match spreadsheet XIRR functions.
Rental Yield Calculator
Gross yield = rent × 12 ÷ property valueNet yield = (rent × (12 − vacant months) − yearly costs) ÷ property value
Results are before income tax, home-loan interest and any change in the property's price.
Mutual Fund Backtester
NAVs are the official daily values published by AMFI. For a SIP, FID buys units on the first NAV date on or after the 1st of each month; a lumpsum buys once on the first NAV date on or after the start. Units = amount ÷ NAV on the purchase date.
Value = total units × NAV on the last date in the period
Return is XIRR across every purchase and the final value. "Worst fall" is the largest drop in the fund's NAV from a previous high, between the first purchase and the valuation date. Results are before exit load, stamp duty and tax, and past returns do not predict future returns.
GST Calculator
Adding GST: GST = amount × rate ÷ 100; total = amount + GSTRemoving GST: GST = total × rate ÷ (100 + rate); amount = total − GST
Within a state (or union territory) the GST is split equally into CGST and SGST/UTGST. Between states it is charged in full as IGST. Amounts are rounded to the nearest paisa, and CGST + SGST always add up to the total GST.
The rate list comes from FID's rates table. The current list has been in force since 22 Sep 2025 (source: cbic-gst.gov.in). It shows the general slabs only. The rate for a particular product or service depends on its HSN or SAC code, so check the CBIC notification for your item. Special rates for some items, such as precious metals, are not listed. Cess, reverse charge, composition schemes and input tax credit are not covered.
Freelancer Income & Rate Calculator
FID starts from the take-home you want and works backwards to the yearly billing that delivers it after business expenses and income tax. It solves this separately for two ways of computing taxable income and recommends the one that needs less billing.
Take-home = receipts − business expenses − income taxPresumptive: taxable income = deemed % × receiptsRegular: taxable income = receipts − business expensesHourly rate = yearly billing ÷ (billable hours per week × (52 − weeks off))
- FY 2026-27: presumptive scheme under section 58, Income-tax Act, 2025. Deemed income 50% of gross receipts. Available when receipts are up to ₹50 L, or ₹75 L when cash receipts are 5% of receipts or less.
- FY 2025-26: presumptive scheme under section 44ADA, Income-tax Act, 1961. Deemed income 50% of gross receipts. Available when receipts are up to ₹50 L, or ₹75 L when cash receipts are 5% of receipts or less.
Tax uses the same slabs, rebate, surcharge and cess as the income tax calculator. Business income gets no standard deduction, and no other deductions are applied. Under the presumptive scheme you may declare more than the deemed share but never have to, and expenses are treated as already covered. If you declare less than the deemed share, you need books of account and possibly a tax audit. The scheme is only for resident individuals and firms (not LLPs) in a specified profession.
Not included: GST, advance-tax interest, other income, and old-regime deductions such as 80C. Receipts are before GST.
Estimates for educational purposes only. Not financial, tax or investment advice.