Stable Numbers
ISA Growth Calculator
Model your ISA with monthly contributions, growth and fees. See the final balance, total paid in, fees, growth and a real-terms figure after inflation. Share your setup and export a full month-by-month schedule.
Used to label schedule months.
Before fees. Applied monthly.
Fees and inflation (optional)
Deducted at the end of each month.
Used to show a real-terms value.
Monthly order is: if timing is start, add the contribution first. Growth is applied, fees are deducted, then any fixed monthly fee is taken. End timing applies growth and fees before adding the contribution.
Show monthly schedule
| # | Date | Start balance | Contribution | Growth | Fees % | Fixed fee | End balance | Real balance |
|---|---|---|---|---|---|---|---|---|
Real balance divides the nominal by cumulative inflation to date using your inflation input.
About this calculator
An ISA shelters growth and income from UK tax. This tool shows how a regular saving habit compounds over time and what fees do to that compounding. You control the starting balance, a steady monthly contribution, the expected gross growth rate and three fee knobs: a platform percentage, a fund Ongoing Charges Figure (OCF) and an optional fixed monthly charge. The calculator separates growth from fees so you can see both clearly rather than folding fees into a single net rate.
Contribution timing matters. If you add money at the start of the month, that cash participates in growth for the full month, which raises the final balance compared with adding at the end. The schedule shows each month’s growth, fees and running balance so you can sense-check the path. The inflation input then converts the final figure into today’s money using a simple monthly inflation model. This is helpful when you are saving for a target that will be paid in real pounds such as a house deposit or retirement spending.
Treat growth as an assumption rather than a promise. Markets move. Fees, on the other hand, are near certain, so reducing them is one lever you control. Use this page to compare providers, fee structures and contribution plans, then copy a share link for your records or export the full schedule as a CSV.
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