Sri Lanka Debenture Return Calculator

A listed corporate debenture is a loan you make to a company — usually a bank or finance company — through the Colombo Stock Exchange. In return the issuer pays a fixed coupon on the face (par) value at set intervals and repays the par value when the debenture matures. The calculator turns those terms into the rupee figures that actually matter, using standard fixed-income arithmetic.

Let F be the face value per debenture, N the number you hold, P the price you paid, c the annual coupon rate, m the coupons per year (1, 2 or 4) and n the years to maturity. The core formulas are:

• Amount invested = N × P
• Coupon per period = N × F × c ÷ m (paid on par, not price)
• Gross annual interest = N × F × c
• Total interest over tenor = N × F × c × n
• Maturity value = N × F; capital gain/loss = N × (F − P)
• Current yield = (F × c) ÷ P
• Approx. YTM = [C + (F − P) ÷ n] ÷ [(F + P) ÷ 2], C = F × c

Because the coupon is fixed to par, buying below par (a discount) lifts your effective yield above the printed rate, and buying above par (a premium) drags it below — which is exactly what the current-yield and YTM lines show. The yield-to-maturity figure is the standard bond approximation; it equals the coupon rate when you buy at par and is flagged as approximate off-par because it averages, rather than discounts, the cashflows.

On tax: since April 1, 2025, interest paid to a resident carries a flat 10% Advance Income Tax deducted at source (IRD Notice PN/IT/2025-01). Net figures apply gross × (1 − 0.1). For residents this AIT is a creditable advance, not a final tax — it is offset against your annual income-tax assessment. If your total assessable income is at or below the Rs 1,800,000personal relief you may file a self-declaration so nothing is withheld (IRD SEC/2025/E/03); the AIT-exempt toggle models that. The same rate is used by this site's Fixed Deposit Interest Tax calculator, so the debenture-versus-FD comparison is apples-to-apples. The tool cross-checks its total interest two ways — the closed-form N × F × c × n and the sum of the period-by-period coupon schedule — and both agree to the rupee.

• IRD — Notice PN/IT/2025-01: Advance Income Tax on interest & discount (10% from 1 April 2025)
• IRD — Circular SEC/2025/E/03: self-declaration procedure for residents within the personal relief
• Colombo Stock Exchange — listed debenture mechanics (par value, coupon, tenor, trading)

The 10% AIT rate, the Rs 1,800,000 personal relief and the self-declaration rule were last cross-checked against the IRD notices on 2026-07-16. This tool surfaces interest and yield math only — it is not investment advice and does not judge an issuer's credit quality. Check the debenture's Fitch Ratings or ICRA Lanka rating and prospectus before investing.